Anesthesiology
1 questionsIn malignant hyperthermia, a genetic mutation in the ryanodine receptor (RYR1) leads to a life-threatening reaction to certain anesthetic agents. What is the primary ionic abnormality caused by this receptor defect?
FMGE 2025 - Anesthesiology FMGE Practice Questions and MCQs
Question 471: In malignant hyperthermia, a genetic mutation in the ryanodine receptor (RYR1) leads to a life-threatening reaction to certain anesthetic agents. What is the primary ionic abnormality caused by this receptor defect?
- A. Increased sodium influx into the muscle cell
- B. Increased potassium uptake into the sarcoplasmic reticulum
- C. Increased calcium release from the sarcoplasmic reticulum (Correct Answer)
- D. Increased chloride efflux from the muscle cell
Explanation: ***Increased calcium release from the sarcoplasmic reticulum*** - The **ryanodine receptor 1 (RYR1)** mutation found in malignant hyperthermia causes the receptor channel on the sarcoplasmic reticulum (SR) to become hypersensitive and spontaneously release large, uncontrolled amounts of **calcium** into the myoplasm upon exposure to triggering agents (e.g., volatile anesthetics like halothane, succinylcholine). - This massive, sustained elevation of intracellular **calcium** drives continuous muscle contraction, leading to muscle rigidity, hypermetabolism, heat production, rhabdomyolysis, and the characteristic life-threatening features of malignant hyperthermia. - Treatment with **dantrolene** works by inhibiting calcium release from the SR, confirming calcium dysregulation as the primary mechanism. *Increased sodium influx into the muscle cell* - Sodium influx is crucial for initiating the muscle action potential via **voltage-gated sodium channels**, but it is not the primary pathological trigger or defining ionic abnormality in malignant hyperthermia. - The sustained muscle contraction in MH is driven by excessive **calcium** in the myoplasm, not sodium influx which is only involved in initial depolarization. *Increased potassium uptake into the sarcoplasmic reticulum* - The sarcoplasmic reticulum's main function is the storage and release of **calcium**, not potassium regulation. - In severe MH, rhabdomyolysis causes **hyperkalemia** due to potassium *efflux* from damaged muscle cells into the bloodstream, not uptake into the SR. *Increased chloride efflux from the muscle cell* - Chloride channels maintain resting membrane potential and regulate cell volume, but their dysregulation is not the central mechanism of malignant hyperthermia. - The life-threatening symptoms of MH (hyperthermia, rigidity, hypermetabolism, acidosis) are a direct consequence of massive, uncontrolled **calcium release** from the SR, not chloride movement.
Biochemistry
4 questionsWhat is the primary protein that binds to thyroxine?
A breastfed infant presents with lethargy, hepatomegaly, and cataracts. Which of the following enzyme deficiencies is most likely responsible for this presentation?
Which vitamin deficiency can lead to lactic acidosis?
Which of the following enzymes is responsible for the immortality of cancer cells?
FMGE 2025 - Biochemistry FMGE Practice Questions and MCQs
Question 471: What is the primary protein that binds to thyroxine?
- A. Follistatin
- B. Transthyretin
- C. Thyroxine-binding globulin (Correct Answer)
- D. Transferrin
Explanation: ***Thyroxine-binding globulin*** - **TBG** is a single chain glycoprotein that is the primary transporter, binding approximately 70-80% of circulating **T4** (thyroxine) and a smaller proportion of T3. - It serves as a high-affinity reservoir, maintaining hormonal homeostasis and contributing to the long **half-life** of T4. *Follistatin* - **Follistatin** binds and inhibits the activity of **activin** and is primarily involved in regulating the release of **FSH** (follicle-stimulating hormone) from the pituitary. - It has no functional role in the systemic transport or binding of thyroid hormones. *Transthyretin* - **Transthyretin** (or prealbumin) is the second most abundant carrier, binding about 10-15% of circulating T4, and is the principal carrier of **retinol** (Vitamin A). - Although it transports T4, its binding affinity and capacity are significantly lower than those of **TBG**, thus it is not the primary binder. *Transferrin* - **Transferrin** is the main plasma protein responsible for transporting **ferric iron (Fe3+)** throughout the body. - Its binding specificity is strictly for iron and does not involve the transport of **thyroxine**.
Question 472: A breastfed infant presents with lethargy, hepatomegaly, and cataracts. Which of the following enzyme deficiencies is most likely responsible for this presentation?
- A. Galactose-1-phosphate uridyltransferase (GALPUT) (Correct Answer)
- B. Galactokinase
- C. Aldolase B
- D. Fructokinase
Explanation: ***Correct: Galactose-1-phosphate uridyltransferase (GALPUT)*** - This deficiency causes **Classic Galactosemia**, the most severe form of galactosemia - Leads to accumulation of toxic metabolites: **galactose-1-phosphate** (causes systemic toxicity) and **galactitol** (causes cataracts) - **Clinical presentation** matches perfectly: breastfed infant (lactose from breast milk is broken down to galactose), lethargy, hepatomegaly, and cataracts - The systemic buildup of **galactose-1-phosphate** causes severe hepatotoxicity, jaundice, and CNS effects (lethargy) - **Galactitol** accumulation in the lens causes osmotic damage leading to cataracts - Treatment requires **complete galactose/lactose elimination** from diet *Incorrect: Galactokinase* - Deficiency causes a **milder form of galactosemia** (Type II) - Presents almost exclusively with **cataracts only** due to galactitol accumulation - Does **NOT** cause accumulation of the highly toxic galactose-1-phosphate - Therefore does **NOT** cause hepatomegaly, liver dysfunction, or systemic symptoms like lethargy - If this were the diagnosis, the infant would only have cataracts without hepatomegaly *Incorrect: Aldolase B* - Deficiency causes **Hereditary Fructose Intolerance (HFI)** - Symptoms occur with **fructose or sucrose** ingestion (typically after weaning when fruits/formula introduced) - Clinical features: vomiting, hypoglycemia, hepatomegaly, and jaundice with fructose exposure - Does **NOT** cause cataracts - Since this is a **breastfed infant** (lactose/galactose, not fructose), and cataracts are present, HFI is ruled out *Incorrect: Fructokinase* - Deficiency causes **Essential Fructosuria**, a completely **benign condition** - Clinically **asymptomatic** - considered a benign inborn error of metabolism - Results in fructose accumulation and urinary excretion without any systemic effects - Does **NOT** cause hepatomegaly, cataracts, lethargy, or any clinical symptoms - Often discovered incidentally on routine urinalysis
Question 473: Which vitamin deficiency can lead to lactic acidosis?
- A. Riboflavin
- B. Thiamine (Correct Answer)
- C. Niacin
- D. Biotin
Explanation: ***Thiamine*** - **Thiamine (Vitamin B1)** is a crucial cofactor for the enzyme **pyruvate dehydrogenase (PDH)**, which converts **pyruvate** to **acetyl-CoA** to enter the Krebs cycle. - When thiamine is deficient, pyruvate cannot be processed efficiently, leading to its accumulation and subsequent shunting into **lactate** via **lactate dehydrogenase**, thus causing **lactic acidosis**, characteristic of **beriberi**. *Riboflavin* - Riboflavin (Vitamin B2) is a precursor for the coenzymes **FAD** and **FMN**, essential for redox reactions, but its deficiency symptoms mainly involve the oral cavity and skin. - Deficiency leads to **angular cheilitis**, **glossitis**, and **corneal vascularization**, and is not the direct cause of severe lactic acidosis. *Niacin* - Niacin (Vitamin B3) is a precursor for **NAD+** and **NADP+**, vital for many metabolic reactions. - Deficiency causes **pellagra**, characterized by the 3 D's: **Dermatitis**, **Diarrhea**, and **Dementia**, not primarily lactic acidosis. *Biotin* - Biotin (Vitamin B7) acts as a coenzyme for **carboxylase enzymes** (e.g., pyruvate carboxylase, acetyl-CoA carboxylase), which are necessary for gluconeogenesis and fatty acid synthesis. - While **pyruvate carboxylase** uses biotin, thiamine deficiency specifically impairs the key step of converting pyruvate to acetyl-CoA (via PDH complex), making it the primary cause of vitamin-deficiency-related lactic acidosis.
Question 474: Which of the following enzymes is responsible for the immortality of cancer cells?
- A. RNA polymerase
- B. Telomerase (Correct Answer)
- C. Helicase
- D. Topoisomerase
Explanation: ***Telomerase*** **Telomerase** is a **ribonucleoprotein enzyme** that adds repetitive DNA sequences (TTAGGG) to the ends of chromosomes (**telomeres**), counteracting the natural shortening that occurs during cell division. The activation of **telomerase** is characteristic of most cancer cells, granting them the ability to divide indefinitely, fulfilling the hallmark of **unlimited replicative potential** (immortality). *Topoisomerase* This enzyme is crucial for relieving the **torsional strain** (supercoiling) in the DNA helix that arises ahead of the replication fork or during transcription. Its primary role is managing DNA structure and integrity, not determining cellular lifespan or **immortality** through **telomere** maintenance. *Helicase* **Helicases** are motor proteins that use energy from ATP hydrolysis to **unwind nucleic acid duplexes** (like the DNA double helix) in fundamental processes such as DNA replication, repair, and transcription. While essential for replication, it does not prevent the gradual loss of terminal DNA sequences (**telomeres**) required for cancer cell immortality. *RNA polymerase* This enzyme is responsible for **transcription**, the process of synthesizing an **RNA molecule** from a DNA template. Its function is focused on gene expression (protein synthesis) and is not directly involved in maintaining the length of **telomeres** or conferring replicative immortality upon cells.
Internal Medicine
1 questionsA man presents with high VLDL and chylomicrons, with eruptive xanthomas. What is the most likely diagnosis?
FMGE 2025 - Internal Medicine FMGE Practice Questions and MCQs
Question 471: A man presents with high VLDL and chylomicrons, with eruptive xanthomas. What is the most likely diagnosis?
- A. Familial hyperlipidemia
- B. Familial dysbetalipoproteinemia
- C. Familial hypertriglyceridemia (Correct Answer)
- D. Familial hypercholesterolemia
Explanation: ***Familial hypertriglyceridemia (Type IV or V hyperlipidemia)*** - This condition presents with **elevated VLDL and chylomicrons**, causing severe hypertriglyceridemia [1] - **Eruptive xanthomas** are pathognomonic for triglyceride levels >1000 mg/dL, appearing as small yellow papules on extensor surfaces and buttocks - Patients are at risk for **acute pancreatitis** due to extreme triglyceride elevation - Treatment includes **fibrates, omega-3 fatty acids, and strict dietary fat restriction** [2] *Familial hyperlipidemia* - This is a non-specific term that could refer to any inherited lipid disorder - Not a precise diagnostic entity used in clinical practice *Familial dysbetalipoproteinemia (Type III)* - Characterized by elevated **IDL (intermediate-density lipoproteins)**, not primarily VLDL + chylomicrons [1] - Presents with **palmar xanthomas (yellowish discoloration of palmar creases)** and tuberoeruptive xanthomas [1] - Different lipid pattern and xanthoma distribution than described *Familial hypercholesterolemia* - Characterized by elevated **LDL cholesterol**, not triglycerides [1] - Presents with **tendinous xanthomas, xanthelasma, and corneal arcus** [1] - Does not cause eruptive xanthomas or chylomicronemia
Microbiology
3 questionsWhich opportunistic pathogen demonstrates a “crushed ping pong ball appearance” on Gomori methenamine stain?
Which antibody is the first to appear and acts fastest during a primary (first) immune response to an infection?
Chocolate agar is primarily used for the isolation of which of the following organisms?
FMGE 2025 - Microbiology FMGE Practice Questions and MCQs
Question 471: Which opportunistic pathogen demonstrates a “crushed ping pong ball appearance” on Gomori methenamine stain?
- A. Cryptococcus neoformans
- B. Pneumocystis jirovecii (Correct Answer)
- C. Aspergillus fumigatus
- D. Histoplasma capsulatum
Explanation: ***Pneumocystis jirovecii*** - This opportunistic fungus classically appears as collapsed, crescent-shaped cysts on **Gomori methenamine silver (GMS) stain**, giving it the pathognomonic **“crushed ping pong ball”** appearance. - It is a common cause of **Pneumocystis pneumonia (PCP)** in immunocompromised individuals, particularly those with advanced HIV infection, and is typically found in the alveolar spaces. *Histoplasma capsulatum* - This dimorphic fungus appears as small, oval yeasts that are characteristically found **intracellularly within macrophages**. - It does not form the collapsed cysts seen with *P. jirovecii* and lacks the “crushed ping pong ball” morphology. *Cryptococcus neoformans* - This yeast is distinguished by its thick **polysaccharide capsule**, which creates a clear halo around the organism on **India ink stain**. - While it can be stained with GMS, it appears as a budding yeast and does not exhibit the collapsed cyst morphology. *Aspergillus fumigatus* - This mold is identified by its characteristic **septate hyphae** that branch at **acute (45-degree) angles**. - It does not form cysts in tissue and has a filamentous structure, which is entirely different from the appearance of *P. jirovecii*.
Question 472: Which antibody is the first to appear and acts fastest during a primary (first) immune response to an infection?
- A. IgE
- B. IgA
- C. IgG
- D. IgM (Correct Answer)
Explanation: ***IgM***- **IgM** is the first antibody isotype produced and secreted by **plasma B cells** following initial exposure to an antigen (primary immune response).- Because it is a **pentamer** (five Y-shaped units), IgM has 10 binding sites, giving it superior efficiency in complement activation, agglutination, and acting as the immediate responder.*IgG*- **IgG** is the most abundant immunoglobulin in the serum and generally appears later than IgM during the primary response.- It is the predominant antibody during the **secondary immune response**, providing long-term immunity and crossing the **placenta**.*IgE*- **IgE** is associated primarily with the initiation of **Type I hypersensitivity reactions** (allergies) by binding to mast cells and basophils.- It is also critical for defense against **helminthic parasites** but is not the first antibody in standard acute infection.*IgA*- **IgA** functions primarily in **mucosal immunity**, being secreted as a dimer into milk, saliva, tears, and mucosal linings (e.g., gut and respiratory tract).- While vital for preventing pathogen entry, it does not lead the kinetics of the initial systemic antibody response.
Question 473: Chocolate agar is primarily used for the isolation of which of the following organisms?
- A. Listeria monocytogenes
- B. Streptococcus pneumoniae
- C. Escherichia coli
- D. Haemophilus influenzae (Correct Answer)
Explanation: ***Haemophilus influenzae*** - *H. influenzae* is a **fastidious** organism requiring **X factor (hemin)** and **V factor (NAD/NADH)** for growth, both of which are supplied by the lysed red blood cells in chocolate agar. - Chocolate agar is essentially **heated blood agar** where the red blood cells have lysed, releasing essential growth factors required by organisms like *Haemophilus spp*. *Listeria monocytogenes* - *Listeria monocytogenes* is a **non-fastidious** organism that typically grows well on routine sheep **Blood Agar** (often showing weak beta-hemolysis). - Isolation of *Listeria* often utilizes cold enrichment or specialized selective media like **Oxford agar** or **PALCAM agar**. *Streptococcus pneumoniae* - *S. pneumoniae* typically grows well on routine **Blood Agar**, where it exhibits characteristic **alpha-hemolysis** (partial lysis resulting in a green discoloration). - While it can grow on chocolate agar, it does not require the specific X and V factors released, making Blood Agar the standard medium for its isolation. *Escherichia coli* - *E. coli* is a non-fastidious, common enteric bacterium that grows easily on non-enriched media like **Nutrient agar**. - It is typically identified using selective and differential media such as **MacConkey agar** (lactose-fermenting pink colonies) or Eosin Methylene Blue (EMB) agar.
Pathology
1 questionsWhich among the following best describes 'Neuropraxia'?
FMGE 2025 - Pathology FMGE Practice Questions and MCQs
Question 471: Which among the following best describes 'Neuropraxia'?
- A. Intact axon; Damaged nerve sheath (Correct Answer)
- B. None of the above
- C. Damaged axon and nerve sheath
- D. Damaged axon; Intact nerve sheath
Explanation: ***Intact axon; Damaged nerve sheath*** - This correctly describes **Neuropraxia**, the mildest form of nerve injury, where there is localized damage to the **myelin sheath** causing a temporary conduction block [1]. - The **axon** and connective tissue layers (**endoneurium**, **perineurium**, and **epineurium**) remain intact, allowing for complete and relatively rapid recovery once the compression is relieved. *Damaged axon; Intact nerve sheath* - This description corresponds to **Axonotmesis**, a more severe injury where the axon is disrupted, leading to **Wallerian degeneration** distal to the lesion [2]. - The surrounding connective tissue sheaths remain intact, which provides a scaffold for axonal regeneration, though recovery is slower and less complete than in neuropraxia. *Damaged axon and nerve sheath* - This describes **Neurotmesis**, the most severe type of nerve injury, involving complete transection of the axon and its surrounding connective tissue sheaths [2]. - Due to the disruption of the entire nerve trunk, spontaneous recovery is unlikely, and **surgical intervention** is often required to restore function. *None of the above* - This option is incorrect as the first option accurately defines **Neuropraxia** according to Seddon's classification of nerve injuries. - The other options describe the more severe forms of nerve injury, **Axonotmesis** and **Neurotmesis**, covering the primary classifications. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, p. 1232. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 109-110.