Common Infections — MCQs
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A 16-year-old boy presents with a 1-week history of sore throat and fever. He has developed a widespread maculopapular rash after taking amoxicillin prescribed by his GP. What is the most likely underlying diagnosis?
A 25-year-old woman presents with a 2-week history of sore throat, fever, and fatigue. She has cervical lymphadenopathy and splenomegaly. Her throat swab is negative for Group A Streptococcus. What is the most likely diagnosis?
A 31-year-old man presents with fever, sore throat, and a widespread maculopapular rash after taking amoxicillin prescribed by his GP. What is the most likely underlying diagnosis?
A 58-year-old man with diabetes presents with severe foot pain and a deep ulcer exposing bone. X-ray shows osteolytic changes. What is the most likely complication?
A 34-year-old woman with Crohn's disease on adalimumab presents with a 10-day history of multiple painful nodules on both shins. The lesions are 2-4cm in diameter, raised, tender, and erythematous without ulceration or pustulation. She reports associated joint pains in her knees and ankles but no fever. Recent colonoscopy showed active inflammation. Blood tests reveal WCC 11.2 × 10⁹/L, CRP 78 mg/L, ESR 65 mm/hr. What is the most likely diagnosis?
Common Infections UK Medical PG Practice Questions and MCQs
Question 1: A 16-year-old boy presents with a 1-week history of sore throat and fever. He has developed a widespread maculopapular rash after taking amoxicillin prescribed by his GP. What is the most likely underlying diagnosis?
- A. Penicillin allergy
- B. Infectious mononucleosis (Correct Answer)
- C. Scarlet fever
- D. Kawasaki disease
- E. Stevens-Johnson syndrome
Explanation: ***Infectious mononucleosis***- The classic triad of **fever**, **pharyngitis** (sore throat), and **lymphadenopathy** in a young patient is highly suggestive of infectious mononucleosis, commonly caused by **Epstein-Barr virus (EBV)**.- A **widespread maculopapular rash** following amoxicillin administration is a very common and characteristic reaction in patients with infectious mononucleosis, often misinterpreted as a penicillin allergy.*Penicillin allergy*- While a rash after amoxicillin can indicate a penicillin allergy, the preceding symptoms of **sore throat and fever** for a week make an underlying infection, specifically mononucleosis, a more likely cause for the rash.- True penicillin allergies often present with **urticaria**, angioedema, or anaphylaxis, rather than a widespread maculopapular rash exacerbated by a viral illness.*Scarlet fever*- Scarlet fever is caused by **Streptococcus pyogenes** and presents with a characteristic **sandpaper-like rash** (finely papular, erythematous) and **strawberry tongue**, which are not described here.- While it causes sore throat and fever, the rash associated with scarlet fever is distinct from a generalized maculopapular rash triggered by amoxicillin in the context of mononucleosis.*Kawasaki disease*- Kawasaki disease primarily affects **young children** (typically under 5 years old) and is characterized by prolonged fever, **conjunctival injection**, **mucosal changes** (strawberry tongue, red lips), **polymorphous rash**, **cervical lymphadenopathy**, and **extremity changes**.- The patient's age (16 years old) and the specific rash reaction to amoxicillin make Kawasaki disease highly unlikely.*Stevens-Johnson syndrome*- **Stevens-Johnson syndrome (SJS)** is a severe mucocutaneous reaction, often drug-induced, characterized by widespread **bullae**, **erosions**, and **mucosal involvement** (oral, ocular, genital) with significant skin detachment (less than 10% total body surface area).- The description of a **widespread maculopapular rash** in this case is not consistent with the severe blistering and erosions typical of SJS.
Question 2: A 25-year-old woman presents with a 2-week history of sore throat, fever, and fatigue. She has cervical lymphadenopathy and splenomegaly. Her throat swab is negative for Group A Streptococcus. What is the most likely diagnosis?
- A. Viral pharyngitis
- B. Infectious mononucleosis (Correct Answer)
- C. Bacterial pharyngitis
- D. Diphtheria
- E. Candidiasis
Explanation: ***Infectious mononucleosis***- The constellation of prolonged **fever**, **pharyngitis**, diffuse **lymphadenopathy**, and **splenomegaly** in a young adult is the classic presentation of primary infection with **Epstein-Barr Virus (EBV)**.- The relatively long duration of symptoms (2 weeks), the presence of **splenomegaly**, and the **negative Group A Strep swab** strongly suggest infectious mononucleosis.*Viral pharyngitis*- Common viral causes (e.g., rhinovirus, adenovirus) usually result in an acute illness, lasting less than 10 days, and do not typically cause sustained systemic symptoms or significant **splenomegaly**.- While presenting with sore throat and fever, non-EBV viral pharyngitis lacks the profound, persistent **fatigue** and notable **lymphadenopathy** seen in infectious mononucleosis.*Bacterial pharyngitis*- This is typically caused by *Streptococcus pyogenes* (Group A Strep), which was **ruled out by the negative throat swab**.- **Bacterial pharyngitis** rarely causes the sustained constitutional symptoms and concurrent **splenomegaly** seen in this case.*Diphtheria*- The hallmark of **diphtheria** is the presence of a thick, adherent, gray-white **pseudomembrane** on the tonsils and pharynx, which is not described in this patient.- It is rare in vaccinated populations and often leads to severe systemic toxicity (e.g., **myocarditis**) rather than the classic infectious mononucleosis triad.*Candidiasis*- Pharyngeal **candidiasis (thrush)** presents as white, easily removable plaques, often favored by antibiotic use or **immunosuppression**.- It is primarily a localized mucosal infection and usually does not cause the fever, systemic illness, or **splenomegaly** seen here.
Question 3: A 31-year-old man presents with fever, sore throat, and a widespread maculopapular rash after taking amoxicillin prescribed by his GP. What is the most likely underlying diagnosis?
- A. Penicillin allergy
- B. Infectious mononucleosis (Correct Answer)
- C. Scarlet fever
- D. Kawasaki disease
- E. Stevens-Johnson syndrome
Explanation: ***Infectious mononucleosis*** - The combination of **fever**, **sore throat**, and a widespread **maculopapular rash** after taking amoxicillin is a classic presentation for **Epstein-Barr virus (EBV)** infection (infectious mononucleosis). - Approximately 80-90% of patients with infectious mononucleosis develop a non-allergic, diffuse rash when treated with **amoxicillin** or **ampicillin**. *Penicillin allergy* - A true **penicillin allergy** (Type I hypersensitivity) typically manifests as rapid onset **urticaria**, angioedema, or anaphylaxis, or a delayed itchy morbilliform rash, usually without the characteristic mononucleosis triad of symptoms. - The rash in mononucleosis patients taking amoxicillin is a **pharmacological interaction** with the underlying viral process, not a typical immunological allergic reaction. *Scarlet fever* - Characterized by a **sandpaper-like erythrodermic rash** and **circumoral pallor**, caused by *Streptococcus pyogenes* erythrogenic toxins. - The current presentation with a maculopapular rash specifically after amoxicillin is not typical of a streptococcal rash and strongly points towards a viral etiology. *Kawasaki disease* - This is a **medium-vessel vasculitis** primarily affecting **children** (typically under 5 years old), making it a highly unlikely diagnosis in a 31-year-old man. - Diagnosis requires persistent fever plus specific criteria like conjunctivitis, oral changes, peripheral extremity changes, lymphadenopathy, and a polymorphous rash. *Stevens-Johnson syndrome* - SJS is a severe, life-threatening **mucocutaneous reaction** characterized by **atypical target lesions** and prominent involvement of **mucous membranes** (oral, ocular, genital). - This condition involves significant **epidermal detachment** (less than 10% of total body surface area) and is distinct from a simple widespread maculopapular rash.
Question 4: A 58-year-old man with diabetes presents with severe foot pain and a deep ulcer exposing bone. X-ray shows osteolytic changes. What is the most likely complication?
- A. Cellulitis
- B. Osteomyelitis (Correct Answer)
- C. Charcot arthropathy
- D. Peripheral arterial disease
- E. Deep vein thrombosis
Explanation: ***Osteomyelitis***- The patient's presentation of a **deep ulcer exposing bone** in the setting of **diabetes**, coupled with **severe foot pain** and **osteolytic changes** on X-ray, are classic indicators of osteomyelitis (bone infection).- **Diabetic foot ulcers** provide a direct pathway for bacterial invasion into the underlying bone, leading to destructive changes visible on imaging like X-rays.*Cellulitis*- Cellulitis is a bacterial infection of the **superficial skin and subcutaneous tissue**, characterized by **erythema**, warmth, and localized swelling.- It typically does not involve the underlying bone and therefore would not present with **bone exposure** or **osteolytic changes** on X-ray.*Charcot arthropathy*- **Charcot arthropathy** is a neuropathic joint degeneration, commonly seen in advanced diabetes, causing progressive joint destruction and deformity, often a **"rocker-bottom" foot**.- While it can lead to foot deformity and subsequent ulceration, it is typically **painless** due to significant neuropathy, contrasting with the patient's **severe pain**, and direct osteolytic changes of infection are not its primary X-ray feature.*Peripheral arterial disease*- **Peripheral arterial disease (PAD)** causes reduced blood flow to the extremities, leading to symptoms like **claudication**, **ischemic ulcers** (often on toes/heels), and rest pain.- While a significant comorbidity in diabetics and a risk factor for ulcers, PAD primarily involves vascular insufficiency and does not directly cause the **osteolytic changes** indicative of bone infection.*Deep vein thrombosis*- **Deep vein thrombosis (DVT)** is a blood clot in a deep vein, typically presenting as **unilateral leg swelling**, pain, and warmth.- It is a vascular issue not primarily associated with ulcers exposing bone, nor does it cause the **osteolytic changes** on a foot X-ray.
Question 5: A 34-year-old woman with Crohn's disease on adalimumab presents with a 10-day history of multiple painful nodules on both shins. The lesions are 2-4cm in diameter, raised, tender, and erythematous without ulceration or pustulation. She reports associated joint pains in her knees and ankles but no fever. Recent colonoscopy showed active inflammation. Blood tests reveal WCC 11.2 × 10⁹/L, CRP 78 mg/L, ESR 65 mm/hr. What is the most likely diagnosis?
- A. Cellulitis secondary to immunosuppression
- B. Pyoderma gangrenosum
- C. Erythema nodosum (Correct Answer)
- D. Sweet's syndrome (acute febrile neutrophilic dermatosis)
- E. Subcutaneous nodular panniculitis from adalimumab injection sites
Explanation: ***Erythema nodosum*** - This patient presents with classic **tender, erythematous nodules** on the **shins** and associated **arthralgia** in the knees and ankles, which is a common extraintestinal manifestation of **Crohn's disease**. - The active intestinal inflammation noted on colonoscopy and elevated **CRP** and **ESR** correlate well with the onset of erythema nodosum, which often reflects underlying disease activity. *Cellulitis secondary to immunosuppression* - Typically presents as a **unilateral**, diffuse area of skin erythema and warmth, often with a spreading border, rather than discrete, **bilateral nodules**. - Usually accompanied by systemic features such as **fever** and significant pain upon touch, which are not explicitly reported here as the primary presenting features. *Pyoderma gangrenosum* - Characterized by rapidly enlarging, **painful ulcers** with **undermined violaceous borders** and purulent bases, whereas this patient has non-ulcerated nodules. - While also associated with **Inflammatory Bowel Disease (IBD)**, its distinctive ulcerative morphology is a key differentiator from the patient's presentation. *Sweet's syndrome (acute febrile neutrophilic dermatosis)* - Typically presents with the sudden onset of painful, edematous, **erythematous plaques** or nodules frequently associated with a **high fever** and marked **peripheral neutrophilia**. - The absence of fever and the nodular presentation without prominent plaques make this diagnosis less likely compared to erythema nodosum. *Subcutaneous nodular panniculitis from adalimumab injection sites* - These reactions would be localized strictly to the **site of injection**, commonly the **abdomen or thighs**, and would not typically manifest as widespread bilateral shin nodules. - Such reactions are usually local inflammatory responses and not typically indicative of a systemic flare-up of Crohn's disease with corresponding elevated inflammatory markers like **CRP** and **ESR**.
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