Two weeks after undergoing allogeneic stem cell transplant for multiple myeloma, a 55-year-old man develops a severely pruritic rash, abdominal cramps, and profuse diarrhea. He appears lethargic. Physical examination shows yellow sclerae. There is a generalized maculopapular rash on his face, trunk, and lower extremities, and desquamation of both soles. His serum alanine aminotransferase is 115 U/L, serum aspartate aminotransferase is 97 U/L, and serum total bilirubin is 2.7 mg/dL. Which of the following is the most likely underlying cause of this patient's condition?
Q2
A 23-year-old woman presents to her primary care provider complaining of diarrhea. She reports a 2 month history of 3-4 bloody stools per day as well as 10 pounds of unexpected weight loss. She has also developed intermittent mild gnawing lower abdominal pain. Her past medical history is unremarkable. She takes no medications and denies any drug allergies. Her family history is notable for colon cancer in her maternal aunt, rheumatoid arthritis in her paternal aunt, and Sjogren syndrome in her paternal grandmother. Her temperature is 99.1°F (37.3°C), blood pressure is 120/85 mmHg, pulse is 85/min, and respirations are 18/min. On exam, she has mild hypogastric tenderness to palpation. A stool guaiac test is positive. Flexible sigmoidoscopy demonstrates hyperemic and friable rectal mucosa. She is started on a medication to address her condition but presents to her physician one week later with a severe sunburn and skin itchiness following limited exposure to sunlight. Which of the following is the mechanism of action of the medication she received?
Q3
During a study on the immune system, an investigator isolates and labels T cells from the cortex of the thymus. The T cells that do not bind cortical epithelial cells expressing MHC molecules undergo apoptosis within 3–4 days. Which of the following best describes the T cells during this phase of differentiation?
Q4
A 28-year-old woman has a follow-up visit with her physician. She was diagnosed with allergic rhinitis and bronchial asthma at 11 years of age. Her regular controller medications include daily high-dose inhaled corticosteroids and montelukast, but she still needs to use a rescue inhaler 3–4 times a week following exercise. She also becomes breathless with moderate exertion. After a thorough evaluation, the physician explains that her medication dosages need to be increased. She declines taking oral corticosteroids daily due to concerns about side effects. The physician prescribes omalizumab, which is administered subcutaneously every 3 weeks. Which of the following best explains the mechanism of action of the new medication that has been added to the controller medications?
Q5
A 50-year-old woman comes to the physician for the evaluation of excessive hair growth on her chin over the past 2 weeks. She also reports progressive enlargement of her gums. Three months ago, she underwent a liver transplantation due to Wilson disease. Following the procedure, the patient was started on transplant rejection prophylaxis. She has a history of poorly-controlled type 2 diabetes mellitus. Temperature is 37°C (98.6°F), pulse is 80/min, respirations are 22/min, and blood pressure is 150/80 mm Hg. Physical examination shows dark-pigmented, coarse hair on the chin, upper lip, and chest. The gingiva and the labial mucosa are swollen. There is a well-healed scar on her right lower abdomen. Which of the following drugs is the most likely cause of this patient's findings?
Q6
A 35-year-old man comes to the physician because of a 6-month history of fatigue and increased sweating at night. He says that he feels “constantly tired” and needs more rest than usual although he sleeps well. In the morning, his sheets are often wet and his skin is clammy. He has not had any sore throat, runny nose, or cough recently. He has not traveled anywhere. Over the past 4 months, he has had a 6.8-kg (15-lb) weight loss, despite having a normal appetite. He does not drink or urinate more than usual. He is 181 cm (5 ft 11 in) tall and weighs 72 kg (159 lb); BMI is 22 kg/m2. His temperature is 37.9°C (100.2°F), pulse is 65/min, and blood pressure is 120/70 mm Hg. Physical examination shows no abnormalities. An HIV screening test and confirmatory test are both positive. The CD4 count is 600 cells/μl and the viral load is 104 copies/mL. Treatment with lamivudine, zidovudine, and indinavir is begun. The patient is at greatest risk for which of the following adverse effects?
Q7
A 66-year-old man comes to the physician because of a 3-month history of constipation and streaks of blood in his stool. He has had a 10-kg (22-lb) weight loss during this period. Colonoscopy shows an exophytic tumor in the sigmoid colon. A CT scan of the abdomen shows liver metastases and enlarged mesenteric and para-aortic lymph nodes. A diagnosis of stage IV colorectal cancer is made, and palliative chemotherapy is initiated. The chemotherapy regimen includes a monoclonal antibody that inhibits tumor growth by preventing ligand binding to a protein directly responsible for epithelial cell proliferation and organogenesis. Which of the following proteins is most likely inhibited by this drug?
Q8
A 24-year-old woman presents to the emergency department because she started experiencing dyspnea and urticaria after dinner. Her symptoms began approximately 15 minutes after eating a new type of shellfish that she has never had before. On physical exam her breathing is labored, and pulmonary auscultation reveals wheezing bilaterally. Given this presentation, she is immediately started on intramuscular epinephrine for treatment of her symptoms. If part of this patient's symptoms were related to the systemic release of certain complement components, which of the following is another function of the responsible component?
Q9
A 37-year-old woman with a history of systemic lupus erythematosus, on prednisone and methotrexate, presents to the dermatology clinic with three weeks of a diffuse, itchy rash. Physical exam is remarkable for small red papules in her bilateral axillae and groin and thin reddish-brown lines in her interdigital spaces. The following skin biopsy is obtained. Which of the following is the most appropriate treatment?
Q10
A 35-year-old woman comes to the physician for the evaluation of fatigue over the past 6 months. During this period, she has also had fever, joint pain, and a recurrent skin rash on her face. She has smoked one pack of cigarettes daily for the past 15 years. Her temperature is 38.5°C (101.3°F), pulse is 90/min, and blood pressure is 130/80 mm Hg. Physical examination shows a facial rash that spares the nasolabial folds and several oral ulcers. Joints of the upper and lower extremities are tender with no reddening or swelling. Laboratory studies show anti-dsDNA antibodies. The patient is diagnosed with systemic lupus erythematosus and treatment of choice is initiated. Eight months later, the patient has weakness in her shoulders and hips. Examination shows slight weakness of the proximal muscles. Deep tendon reflexes are 2+ bilaterally. Laboratory studies show normal erythrocyte sedimentation rate and creatine kinase. Which of the following is the most likely underlying cause of this patient's symptoms?
Immunotherapies and checkpoint inhibitors US Medical PG Practice Questions and MCQs
Question 1: Two weeks after undergoing allogeneic stem cell transplant for multiple myeloma, a 55-year-old man develops a severely pruritic rash, abdominal cramps, and profuse diarrhea. He appears lethargic. Physical examination shows yellow sclerae. There is a generalized maculopapular rash on his face, trunk, and lower extremities, and desquamation of both soles. His serum alanine aminotransferase is 115 U/L, serum aspartate aminotransferase is 97 U/L, and serum total bilirubin is 2.7 mg/dL. Which of the following is the most likely underlying cause of this patient's condition?
A. Preformed cytotoxic anti-HLA antibodies
B. Proliferating transplanted B cells
C. Activated recipient T cells
D. Donor T cells in the graft (Correct Answer)
E. Newly formed anti-HLA antibodies
Explanation: ***Donor T cells in the graft***
- The symptoms (rash, GI symptoms, liver dysfunction) after an allogeneic stem cell transplant are classic signs of **acute graft-versus-host disease (GVHD)**. This condition occurs when **immunocompetent T cells from the donor graft** recognize the recipient's tissues as foreign and mount an immune attack.
- The rapid onset within two weeks post-transplant, elevated liver enzymes, jaundice (**yellow sclerae**, **elevated bilirubin**), severe pruritic rash, and GI symptoms (**abdominal cramps**, **profuse diarrhea**) are all characteristic manifestations of acute GVHD.
*Preformed cytotoxic anti-HLA antibodies*
- Preformed antibodies would typically cause **hyperacute rejection**, which occurs within minutes to hours of transplantation and involves widespread thrombosis and necrosis of the graft, not the systemic symptoms seen here.
- This reaction is mediated by the recipient's antibodies attacking donor antigens, leading to immediate graft failure.
*Proliferating transplanted B cells*
- Transplanted B cells can contribute to chronic GVHD through antibody production, but they are not the primary mediators of **acute GVHD**; acute GVHD is predominantly a T cell-mediated process.
- Proliferation of donor B cells is more commonly associated with post-transplant lymphoproliferative disorders (PTLD) or chronic GVHD, not the acute presentation described.
*Activated recipient T cells*
- In an allogeneic transplant, the recipient's immune system is usually heavily suppressed beforehand to prevent host-versus-graft rejection.
- If recipient T cells were active, they would primarily cause **rejection of the donor stem cells** (graft rejection), not the systemic symptoms of GVHD, which is a reaction of the donor cells against the host.
*Newly formed anti-HLA antibodies*
- Newly formed antibodies the recipient develops against the donor's HLA antigens would cause graft rejection, a process often delayed but not presenting as the widespread organ damage of acute GVHD.
- These antibodies are part of the host's attempt to reject the foreign graft, not the donor cells attacking the host.
Question 2: A 23-year-old woman presents to her primary care provider complaining of diarrhea. She reports a 2 month history of 3-4 bloody stools per day as well as 10 pounds of unexpected weight loss. She has also developed intermittent mild gnawing lower abdominal pain. Her past medical history is unremarkable. She takes no medications and denies any drug allergies. Her family history is notable for colon cancer in her maternal aunt, rheumatoid arthritis in her paternal aunt, and Sjogren syndrome in her paternal grandmother. Her temperature is 99.1°F (37.3°C), blood pressure is 120/85 mmHg, pulse is 85/min, and respirations are 18/min. On exam, she has mild hypogastric tenderness to palpation. A stool guaiac test is positive. Flexible sigmoidoscopy demonstrates hyperemic and friable rectal mucosa. She is started on a medication to address her condition but presents to her physician one week later with a severe sunburn and skin itchiness following limited exposure to sunlight. Which of the following is the mechanism of action of the medication she received?
A. Dihydrofolate reductase inhibitor
B. NF-kB inhibitor (Correct Answer)
C. COX inhibitor
D. Calcineurin inhibitor
E. DNA gyrase inhibitor
Explanation: ***NF-κB inhibitor***
- The patient's symptoms (bloody diarrhea, weight loss, abdominal pain, friable rectal mucosa) are highly suggestive of **ulcerative colitis**
- **Sulfasalazine**, a 5-aminosalicylate (5-ASA) drug, is a common first-line treatment for mild-to-moderate ulcerative colitis
- The active metabolite **mesalamine** exerts its anti-inflammatory effects primarily through **inhibition of NF-κB**, a key transcription factor that regulates inflammatory cytokine production
- The **sulfapyridine** component is responsible for the photosensitivity reaction (severe sunburn and skin itchiness after sun exposure) that this patient experienced
- Other mechanisms include prostaglandin inhibition, free radical scavenging, and modulation of leukocyte function, but **NF-κB inhibition is the predominant mechanism**
*COX inhibitor*
- While mesalamine does have some cyclooxygenase (COX) inhibitory activity and reduces prostaglandin synthesis, this is a **secondary mechanism** of action
- The primary anti-inflammatory effect of 5-ASA drugs in inflammatory bowel disease is through **NF-κB inhibition**, not COX inhibition
- Traditional NSAIDs (pure COX inhibitors) can actually worsen IBD symptoms, highlighting that COX inhibition alone is not the therapeutic mechanism
*Dihydrofolate reductase inhibitor*
- This mechanism describes **methotrexate**, an immunosuppressant used in more severe or refractory cases of inflammatory bowel disease, but not typically as a first-line agent
- Methotrexate is not associated with photosensitivity reactions in the manner seen with sulfasalazine
*Calcineurin inhibitor*
- **Calcineurin inhibitors** such as **cyclosporine** or **tacrolimus** are potent immunosuppressants typically reserved for severe, refractory cases of inflammatory bowel disease
- Their side effect profile includes nephrotoxicity, hypertension, and hirsutism, but not the characteristic photosensitivity seen with sulfasalazine
*DNA gyrase inhibitor*
- **DNA gyrase inhibitors** (fluoroquinolones) are antibiotics used to treat bacterial infections
- These are not used as primary treatment for inflammatory bowel disease, which is an immune-mediated condition
- While fluoroquinolones can cause photosensitivity, they would not be prescribed for ulcerative colitis management
Question 3: During a study on the immune system, an investigator isolates and labels T cells from the cortex of the thymus. The T cells that do not bind cortical epithelial cells expressing MHC molecules undergo apoptosis within 3–4 days. Which of the following best describes the T cells during this phase of differentiation?
A. CD4+
B. CD4+ and CD8+ (Correct Answer)
C. T cell precursor
D. CD8+
E. Th2
Explanation: ***CD4+ and CD8+***
- In the **thymic cortex**, T cells undergo **positive selection**, where only T cells that can bind dimly to self-MHC molecules survive.
- At this stage, cortical thymocytes are typically **double-positive**, expressing both **CD4** and **CD8** co-receptors.
*CD4+*
- While CD4+ T cells are a mature T cell subset, **positive selection** in the cortex involves cells that are still expressing both co-receptors before lineage commitment.
- T cells that exclusively express CD4 have already undergone **lineage commitment** and generally exit the cortex for the medulla if they pass positive selection.
*T cell precursor*
- **T cell precursors** (prothymocytes and early thymocytes) enter the thymus and develop in the subcapsular region before migrating to the cortex.
- They are typically **double-negative** (CD4-CD8-) and have not yet rearranged their TCR genes or expressed CD4/CD8.
*CD8+*
- Similar to CD4+, CD8+ T cells represent a **mature T cell subset** that has already committed to the cytotoxic lineage.
- During positive selection in the cortex, T cells are still in the **double-positive** stage (CD4+CD8+) before differentiating into single-positive cells.
*Th2*
- **Th2 cells** (T helper type 2 cells) are a subset of mature CD4+ T cells that differentiate in the periphery after activation.
- They are not found in the thymus differentiating during the **positive selection** phase in the cortex.
Question 4: A 28-year-old woman has a follow-up visit with her physician. She was diagnosed with allergic rhinitis and bronchial asthma at 11 years of age. Her regular controller medications include daily high-dose inhaled corticosteroids and montelukast, but she still needs to use a rescue inhaler 3–4 times a week following exercise. She also becomes breathless with moderate exertion. After a thorough evaluation, the physician explains that her medication dosages need to be increased. She declines taking oral corticosteroids daily due to concerns about side effects. The physician prescribes omalizumab, which is administered subcutaneously every 3 weeks. Which of the following best explains the mechanism of action of the new medication that has been added to the controller medications?
A. Prevention of binding of IgE antibodies to mast cell receptors (Correct Answer)
B. Inhibition of synthesis of interleukin-4 (IL-4)
C. Inhibition of synthesis of IgE antibodies
D. Selective binding to interleukin-3 (IL-3) and inhibition of its actions
E. Prevention of binding of interleukin-5 (IL-5) to its receptors
Explanation: ***Prevention of binding of IgE antibodies to mast cell receptors***
- **Omalizumab** is a **monoclonal antibody** that specifically targets and binds to **free IgE** in the bloodstream, preventing it from attaching to high-affinity IgE receptors on **mast cells** and **basophils**.
- By reducing surface IgE, omalizumab **downregulates IgE receptors** on these cells, thereby reducing the release of inflammatory mediators upon allergen exposure, which is beneficial in **allergic asthma** uncontrolled by standard therapies.
*Inhibition of synthesis of interleukin-4 (IL-4)*
- **IL-4** is a cytokine primarily involved in **Th2 differentiation** and **IgE class switching**, but omalizumab's action is not directly blocking its synthesis.
- While *omalizumab* indirectly reduces IgE levels, its primary mechanism isn't to inhibit the production of IL-4 itself, but rather to prevent the effects of existing IgE.
*Inhibition of synthesis of IgE antibodies*
- **Omalizumab** does not inhibit the *synthesis* of IgE antibodies; instead, it binds to already synthesized **free IgE** circulating in the blood.
- This binding effectively neutralizes IgE, preventing it from contributing to the allergic cascade, but it doesn't stop B cells from producing more IgE.
*Selective binding to interleukin-3 (IL-3) and inhibition of its actions*
- **IL-3** is a cytokine involved in the growth and differentiation of various **hematopoietic cells**, including mast cells and basophils, but it is not the target of omalizumab.
- Omalizumab specifically targets **IgE** and has no known direct action on IL-3 signaling pathways.
*Prevention of binding of interleukin-5 (IL-5) to its receptors*
- **IL-5** is a key cytokine in the **eosinophilic inflammatory pathway** and is targeted by other therapies (e.g., mepolizumab, reslizumab) used for severe eosinophilic asthma.
- Omalizumab's mechanism is distinct, focusing on **IgE-mediated inflammation** rather than direct eosinophil control.
Question 5: A 50-year-old woman comes to the physician for the evaluation of excessive hair growth on her chin over the past 2 weeks. She also reports progressive enlargement of her gums. Three months ago, she underwent a liver transplantation due to Wilson disease. Following the procedure, the patient was started on transplant rejection prophylaxis. She has a history of poorly-controlled type 2 diabetes mellitus. Temperature is 37°C (98.6°F), pulse is 80/min, respirations are 22/min, and blood pressure is 150/80 mm Hg. Physical examination shows dark-pigmented, coarse hair on the chin, upper lip, and chest. The gingiva and the labial mucosa are swollen. There is a well-healed scar on her right lower abdomen. Which of the following drugs is the most likely cause of this patient's findings?
A. Daclizumab
B. Cyclosporine (Correct Answer)
C. Sirolimus
D. Methotrexate
E. Tacrolimus
Explanation: **Cyclosporine**
* This patient's **combination of hirsutism** (excessive hair growth) **and gingival hyperplasia** (gum enlargement) is the classic presentation of cyclosporine toxicity, an immunosuppressant commonly used for transplant rejection prophylaxis.
* Cyclosporine is a **calcineurin inhibitor** that prevents T-cell activation and is highly effective in preventing graft rejection.
* The **simultaneous presence of both hirsutism and prominent gingival hyperplasia** is particularly characteristic of cyclosporine.
*Daclizumab*
* **Daclizumab** is a **monoclonal antibody** targeting the IL-2 receptor, which was previously used for transplant prophylaxis but has been discontinued for this indication.
* It is not associated with hirsutism or gingival hyperplasia.
*Sirolimus*
* **Sirolimus** is an **mTOR inhibitor** used as an immunosuppressant, known for side effects like hyperlipidemia, myelosuppression, and delayed wound healing.
* It does **not** typically cause hirsutism or gingival hyperplasia.
*Methotrexate*
* **Methotrexate** is an **antimetabolite** and immunosuppressant commonly used in autoimmune diseases and cancer, with side effects including bone marrow suppression, mucositis, and liver toxicity.
* Hirsutism and gingival hyperplasia are **not** characteristic side effects of methotrexate.
*Tacrolimus*
* **Tacrolimus** is another **calcineurin inhibitor**, similar to cyclosporine, but with a different side effect profile. While tacrolimus can cause hirsutism, **gingival hyperplasia is significantly less common** with tacrolimus compared to cyclosporine.
* The **presence of prominent gingival hyperplasia alongside hirsutism strongly favors cyclosporine** over tacrolimus.
* Tacrolimus is more commonly associated with **neurotoxicity** (e.g., tremor) and **nephrotoxicity**.
Question 6: A 35-year-old man comes to the physician because of a 6-month history of fatigue and increased sweating at night. He says that he feels “constantly tired” and needs more rest than usual although he sleeps well. In the morning, his sheets are often wet and his skin is clammy. He has not had any sore throat, runny nose, or cough recently. He has not traveled anywhere. Over the past 4 months, he has had a 6.8-kg (15-lb) weight loss, despite having a normal appetite. He does not drink or urinate more than usual. He is 181 cm (5 ft 11 in) tall and weighs 72 kg (159 lb); BMI is 22 kg/m2. His temperature is 37.9°C (100.2°F), pulse is 65/min, and blood pressure is 120/70 mm Hg. Physical examination shows no abnormalities. An HIV screening test and confirmatory test are both positive. The CD4 count is 600 cells/μl and the viral load is 104 copies/mL. Treatment with lamivudine, zidovudine, and indinavir is begun. The patient is at greatest risk for which of the following adverse effects?
A. Urolithiasis (Correct Answer)
B. Stevens-Johnson syndrome
C. Hypersensitivity reaction
D. Chronic kidney disease
E. Pancreatitis
Explanation: ***Urolithiasis***
- The patient is receiving **indinavir**, a protease inhibitor known to cause **nephrolithiasis** (kidney stones) due to the drug's poor solubility.
- Patients on indinavir should be well-hydrated to reduce the risk of stone formation.
*Stevens-Johnson syndrome*
- This severe skin reaction is more commonly associated with non-nucleoside reverse transcriptase inhibitors (NNRTIs) like **nevirapine** and **efavirenz**, or with sulfonamide antibiotics, rather than indinavir.
- While possible with many drugs, it is not the *greatest risk* among the options for this specific regimen.
*Hypersensitivity reaction*
- While hypersensitivity can occur with many drugs, particularly abacavir (an NRTI not included in this regimen), it is not the most prominent or specific adverse effect for the given combination, especially indinavir.
- Symptoms usually include fever, rash, and multi-organ involvement, which can be acute.
*Chronic kidney disease*
- While some antiretrovirals, particularly **tenofovir disoproxil fumarate (TDF)**, can cause renal tubular dysfunction and lead to chronic kidney disease, TDF is not part of this patient's regimen.
- Indinavir's primary renal complication is acute stone formation, not typically chronic kidney disease in the absence of pre-existing conditions or other nephrotoxic drugs.
*Pancreatitis*
- Pancreatitis is a known adverse effect of some NRTIs, particularly **didanosine** and **stavudine**, neither of which are in this patient's treatment plan.
- Lamivudine and zidovudine have a lower risk of pancreatitis compared to other NRTIs.
Question 7: A 66-year-old man comes to the physician because of a 3-month history of constipation and streaks of blood in his stool. He has had a 10-kg (22-lb) weight loss during this period. Colonoscopy shows an exophytic tumor in the sigmoid colon. A CT scan of the abdomen shows liver metastases and enlarged mesenteric and para-aortic lymph nodes. A diagnosis of stage IV colorectal cancer is made, and palliative chemotherapy is initiated. The chemotherapy regimen includes a monoclonal antibody that inhibits tumor growth by preventing ligand binding to a protein directly responsible for epithelial cell proliferation and organogenesis. Which of the following proteins is most likely inhibited by this drug?
A. VEGF
B. TNF-α
C. EGFR (Correct Answer)
D. ALK
E. CD52
Explanation: ***EGFR***
- The description of a monoclonal antibody preventing ligand binding to a protein responsible for **epithelial cell proliferation** and organogenesis strongly points to the **epidermal growth factor receptor (EGFR)**.
- EGFR is highly expressed in many colorectal cancers and its activation by ligands like EGF promotes cell growth, survival, and metastasis. Inhibiting it reduces tumor progression.
*VEGF*
- **Vascular endothelial growth factor (VEGF)** is primarily involved in **angiogenesis**, the formation of new blood vessels.
- While anti-VEGF therapies (e.g., bevacizumab) are used in colorectal cancer, their mechanism is inhibiting blood supply to the tumor, not directly blocking a receptor responsible for epithelial cell proliferation as described.
*TNF-α*
- **Tumor necrosis factor-alpha (TNF-α)** is a **cytokine** primarily involved in inflammation and immune responses.
- Antibodies against TNF-α (e.g., infliximab) are used in inflammatory conditions like Crohn's disease, not typically as targeted therapy for colorectal cancer directly inhibiting epithelial proliferation.
*ALK*
- **Anaplastic lymphoma kinase (ALK)** is a **receptor tyrosine kinase** often implicated in lung cancer and lymphomas.
- ALK rearrangements lead to oncogenic fusion proteins, but it is not a primary target for widespread epithelial cell proliferation in colorectal cancer.
*CD52*
- **CD52** is a glycoprotein found on the surface of various immune cells, including lymphocytes.
- Antibodies targeting CD52 (e.g., alemtuzumab) are used in certain leukemias and lymphomas to deplete these cells, not for inhibiting epithelial cell proliferation in solid tumors.
Question 8: A 24-year-old woman presents to the emergency department because she started experiencing dyspnea and urticaria after dinner. Her symptoms began approximately 15 minutes after eating a new type of shellfish that she has never had before. On physical exam her breathing is labored, and pulmonary auscultation reveals wheezing bilaterally. Given this presentation, she is immediately started on intramuscular epinephrine for treatment of her symptoms. If part of this patient's symptoms were related to the systemic release of certain complement components, which of the following is another function of the responsible component?
A. Chemotaxis (Correct Answer)
B. Direct cytolysis
C. Inhibition of kallikrein activation
D. Clearance of immune complexes
E. Opsonization of pathogens
Explanation: **Chemotaxis**
- The patient's symptoms are consistent with **anaphylaxis**, an IgE-mediated hypersensitivity reaction that causes mast cell degranulation.
- During anaphylaxis, mast cells release mediators that can activate the **complement system**, producing anaphylatoxins like C3a and C5a. **C5a** is a potent **chemotactic factor** for neutrophils and macrophages, attracting them to the site of inflammation.
*Direct cytolysis*
- **Direct cytolysis** is primarily mediated by the **membrane attack complex (MAC)**, formed by C5b-C9.
- While complement activation occurs in anaphylaxis, the immediate severe symptoms like urticaria and bronchospasm are predominantly due to mast cell degranulation and the release of histamine and other mediators, not direct cell lysis by MAC which occurs in later stages or different contexts.
*Inhibition of kallikrein activation*
- **Kallikrein activation** is inhibited by **C1 esterase inhibitor (C1-INH)**.
- A deficiency in C1-INH leads to conditions like **hereditary angioedema**, which is distinct from the type I hypersensitivity reaction (anaphylaxis) described in the patient.
*Clearance of immune complexes*
- **Clearance of immune complexes** is a function primarily associated with **C3b** binding to immune complexes, allowing their uptake by phagocytes or transport to the liver and spleen.
- While immune complexes are involved in other types of hypersensitivity reactions, they are not the primary mechanism or a direct complement component involved in the acute allergic reaction due to shellfish.
*Opsonization of pathogens*
- **Opsonization** is the process by which pathogens are tagged for phagocytosis, chiefly performed by **C3b** and antibodies.
- While complement plays a role in host defense, opsonization is not the function of the complement components (C3a, C5a) primarily responsible for the anaphylactoid reactions seen in this patient's presentation.
Question 9: A 37-year-old woman with a history of systemic lupus erythematosus, on prednisone and methotrexate, presents to the dermatology clinic with three weeks of a diffuse, itchy rash. Physical exam is remarkable for small red papules in her bilateral axillae and groin and thin reddish-brown lines in her interdigital spaces. The following skin biopsy is obtained. Which of the following is the most appropriate treatment?
A. Capsaicin cream
B. Ketoconazole cream
C. Permethrin cream (Correct Answer)
D. Hydrocortisone cream
E. Nystatin cream
Explanation: ***Permethrin cream***
- The patient's presentation with **diffuse itchy rash**, small red papules in the axillae and groin, and **reddish-brown lines in interdigital spaces (burrows)** is classic for **scabies**.
- **Permethrin 5% cream** is the **first-line treatment** for scabies due to its efficacy as a **scabicidal agent** by disrupting the parasite's nervous system.
- The patient's **immunocompromised status** (on prednisone and methotrexate) increases risk for **crusted (Norwegian) scabies**, but permethrin remains the primary topical treatment; severe cases may require addition of oral ivermectin.
*Capsaicin cream*
- Capsaicin cream is used for **neuropathic pain** and often causes a burning sensation, making it unsuitable for a pruritic rash caused by mites.
- It does not have any **antiparasitic properties** and would not treat the underlying cause of scabies.
*Ketoconazole cream*
- Ketoconazole is an **antifungal agent** used to treat conditions like candidiasis or tinea infections.
- The clinical presentation is not suggestive of a fungal infection, and ketoconazole would be ineffective against scabies mites.
*Hydrocortisone cream*
- Hydrocortisone is a **topical corticosteroid** used to reduce inflammation and itching associated with various dermatoses.
- While it may temporarily relieve itching, it would not eradicate the **scabies mites** and their eggs, leading to recurrence.
- Using corticosteroids alone in an **already immunocompromised patient** could worsen the infestation.
*Nystatin cream*
- Nystatin is another **antifungal medication** primarily used for cutaneous candidiasis.
- It has no activity against parasitic infestations such as scabies and would therefore be an inappropriate treatment.
Question 10: A 35-year-old woman comes to the physician for the evaluation of fatigue over the past 6 months. During this period, she has also had fever, joint pain, and a recurrent skin rash on her face. She has smoked one pack of cigarettes daily for the past 15 years. Her temperature is 38.5°C (101.3°F), pulse is 90/min, and blood pressure is 130/80 mm Hg. Physical examination shows a facial rash that spares the nasolabial folds and several oral ulcers. Joints of the upper and lower extremities are tender with no reddening or swelling. Laboratory studies show anti-dsDNA antibodies. The patient is diagnosed with systemic lupus erythematosus and treatment of choice is initiated. Eight months later, the patient has weakness in her shoulders and hips. Examination shows slight weakness of the proximal muscles. Deep tendon reflexes are 2+ bilaterally. Laboratory studies show normal erythrocyte sedimentation rate and creatine kinase. Which of the following is the most likely underlying cause of this patient's symptoms?
A. Dystrophin gene mutation
B. Adverse effect of medication (Correct Answer)
C. Upper and lower motor neuron degeneration
D. Autoantibodies against postsynaptic acetylcholine receptors
E. Autoantibodies against myelin
Explanation: ***Adverse effect of medication***
- The patient was diagnosed with **systemic lupus erythematosus (SLE)** and started on treatment. **Glucocorticoids** are a common treatment for SLE, and high doses can cause **proximal muscle weakness (steroid myopathy)**.
- The combination of normal ESR and CK, along with symmetrical proximal weakness, is characteristic of steroid-induced myopathy.
*Dystrophin gene mutation*
- **Dystrophinopathies** (e.g., Duchenne or Becker muscular dystrophy) are typically **genetic disorders** that manifest much earlier in life with progressive muscle weakness and elevated CK.
- This patient's symptoms developed acutely after SLE treatment and laboratory findings do not support a genetic muscular dystrophy.
*Upper and lower motor neuron degeneration*
- This describes conditions like **amyotrophic lateral sclerosis (ALS)**, which would feature both **upper motor neuron signs** (e.g., spasticity, hyperreflexia) and **lower motor neuron signs** (e.g., atrophy, fasciculations).
- The patient only shows symmetrical proximal weakness with normal deep tendon reflexes, and no signs of either upper or lower motor neuron disease.
*Autoantibodies against postsynaptic acetylcholine receptors*
- This is the hallmark of **myasthenia gravis**, which causes **fluctuating muscle weakness** that worsens with activity and improves with rest, and often affects ocular and bulbar muscles.
- Myasthenia gravis is less likely given the presentation of gradual, persistent proximal weakness following SLE treatment.
*Autoantibodies against myelin*
- This is characteristic of **demyelinating diseases** like **multiple sclerosis (MS)** or **Guillain-Barré syndrome (GBS)**. These conditions cause various neurological deficits including sensory disturbances, ataxia, or flaccid paralysis (GBS).
- The patient's symptoms are confined to muscle weakness without other neurological signs, and normal deep tendon reflexes argue against these conditions.
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