FIRST INTERNAL ASSESSMENT - 3rd Professional MBBS: Complete Answers

Q1. 24-year-old male, itching over groin and inner thighs for 3 months. Multiple annular erythematous plaques with active scaly margins and central clearing.

a) Most likely diagnosis (1 mark)

b) Two common causative organisms (1 mark)

1. Trichophyton rubrum (most common overall)
2. Epidermophyton floccosum

c) Two bedside/laboratory investigations to confirm diagnosis (2 marks)

1. KOH mount (Potassium Hydroxide preparation) - bedside test: skin scrapings from the active scaly margin are dissolved in 10-20% KOH and examined microscopically for fungal hyphae (septate branching hyphae = dermatophyte infection)
2. Fungal culture (Sabouraud Dextrose Agar) - definitive laboratory test identifying the specific causative dermatophyte species

d) Treatment - one topical + one systemic antifungal (2 marks)

• Topical: Clotrimazole 1% cream applied twice daily for 2-4 weeks (alternatively: terbinafine cream, miconazole, or ketoconazole cream)
• Systemic: Oral terbinafine 250 mg once daily for 2 weeks (alternatively: itraconazole 200 mg/day for 1 week, or fluconazole 150 mg weekly for 2-4 weeks)

Q2. 10-year-old child, recurrent itchy lesions in flexures of elbows and knees since early childhood. Personal history of allergic rhinitis.

a) Most likely diagnosis (2 marks)

b) Two factors in etiopathogenesis (2 marks)

1. Immunological/genetic dysregulation - Th2 skewed immune response with elevated IgE: There is a genetic predisposition causing a polarized Th2 lymphocyte response, resulting in excess IL-4, IL-5, IL-13, and markedly raised serum IgE levels, leading to sensitization, mast cell activation, and eosinophilia. This drives the allergic inflammation.
2. Epidermal barrier dysfunction (filaggrin gene mutation): Loss-of-function mutations in the FLG gene encoding filaggrin reduce the skin's barrier integrity, causing increased trans-epidermal water loss (TEWL), skin dryness, and enhanced allergen penetration - which in turn triggers further immune activation.

c) Management - one topical + two systemic agents (2 marks)

• Topical: Topical corticosteroids (e.g., hydrocortisone 1% for mild; betamethasone valerate for moderate-severe) applied to affected areas to reduce inflammation. Alternatively, topical calcineurin inhibitors (tacrolimus/pimecrolimus) for sensitive areas.
• Systemic agent 1: Oral antihistamines (e.g., cetirizine or hydroxyzine) - to control pruritus, especially at night
• Systemic agent 2: Oral corticosteroids (e.g., prednisolone) for acute severe flares; or cyclosporine (immunosuppressant) for chronic severe/refractory cases

Q3. 35-year-old man, hypopigmented patch over forearm + loss of sensation + thickening of ulnar nerve

a) Most likely diagnosis (1 mark)

b) Two cardinal signs of leprosy (1 mark)

1. Hypopigmented (or erythematous) skin lesion(s) with definite loss of sensation
2. Thickened peripheral nerve (e.g., ulnar, radial cutaneous, common peroneal, posterior tibial, facial, great auricular nerve)
3. Demonstration of acid-fast bacilli (AFB) in slit-skin smear (sometimes counted as a third cardinal sign)

c) Two investigations (bedside/laboratory) for confirmation (2 marks)

1. Slit-Skin Smear (SSS) - bedside: a small incision is made at the lesion site/ear lobe, tissue fluid smear stained with Ziehl-Neelsen stain to detect AFB (Mycobacterium leprae). Gives the Bacteriological Index (BI).
2. Skin biopsy - histopathological examination showing granuloma type (tuberculoid granuloma in TT/BT; foamy macrophages/Virchow cells laden with AFB in LL leprosy). Alternatively: Lepromin (Mitsuda) test - intradermal injection to assess cell-mediated immunity (positive in tuberculoid, negative in lepromatous).

d) WHO-recommended treatment regimen (2 marks)

Q4. 28-year-old sexually active man, single painless ulcer on genitalia for 10 days. Clean-based indurated ulcer + non-tender inguinal lymphadenopathy.

a) Most likely diagnosis and stage of disease (2 marks)

• Diagnosis: Primary Syphilis (caused by Treponema pallidum)
• Stage: Primary stage

• Single painless indurated ulcer = syphilitic chancre (the "clean-based indurated ulcer" with rolled edges)
• Non-tender inguinal lymphadenopathy = regional adenopathy (firm, rubbery, non-tender nodes)
• Sexually active, ulcer present for 10 days (incubation 10-90 days, average 3 weeks)

Note on Q4: The image is partially cut off - only part (a) is visible. If there are further parts (b, c, d), they likely ask about: (b) investigations - darkfield microscopy / VDRL + TPHA; (c) treatment - benzathine penicillin G 2.4 million units IM single dose; (d) contacts/partner tracing.

Quick Reference Summary

Exam Paper (Continued) - Complete Answers

Q4 (Continued) - Primary Syphilis in a 28-year-old male

b) Two investigations to confirm the diagnosis (2 marks)

1. Darkfield microscopy - fluid/exudate from the base of the chancre is examined under darkfield microscope to directly visualize the motile spirochetes (Treponema pallidum). This is the most specific bedside method for primary syphilis.
2. Serological tests:
   • Non-treponemal test: VDRL (Venereal Disease Research Laboratory) or RPR (Rapid Plasma Reagin) - a screening test; positive in ~75% of primary syphilis cases (may be negative very early)
   • Treponemal-specific test: FTA-ABS (Fluorescent Treponemal Antibody Absorption) or TPHA (Treponema pallidum Haemagglutination Assay) - the most sensitive and specific confirmatory serological test

c) Drug of choice and dose for treatment (1 mark)

• Given as a single IM injection for primary and secondary syphilis
• In penicillin allergy: Doxycycline 100 mg orally twice daily for 14 days (or Azithromycin 2 g orally single dose)

d) One measure for prevention of transmission from mother to child (1 mark)

• All pregnant women should be screened for syphilis at the first antenatal visit
• Infected mothers are treated with the appropriate penicillin regimen according to stage of disease
• This prevents transplacental transmission of T. pallidum and eliminates congenital syphilis

Q5. 30-year-old woman developed sudden onset itchy wheals all over the body after taking an antibiotic. Lesions disappeared within a few hours without leaving any marks. She also developed swelling of the lips.

a) Most likely diagnoses (2 marks)

1. Acute Urticaria (drug-induced / allergic urticaria) - the sudden-onset pruritic wheals that disappear completely within hours without any residual marks (no scarring or pigmentation) are classic for urticaria
2. Angioedema - the swelling of the lips represents angioedema (deeper dermal/subcutaneous swelling affecting the face, lips, tongue), which frequently accompanies urticaria

Key diagnostic feature: Wheals = evanescent (disappear within 24 hours), no marks left = rules out vasculitis or other urticarial syndromes.

b) Two common precipitating factors for urticaria/angioedema (2 marks)

1. Drugs - the most common drug causes include:
   • Antibiotics (especially penicillins, cephalosporins - IgE-mediated Type I hypersensitivity)
   • NSAIDs/Aspirin (non-immunological, via COX-1 inhibition → increased leukotriene production)
   • ACE inhibitors (cause bradykinin-mediated angioedema)
2. Foods - common food triggers: nuts (peanuts, tree nuts), shellfish, eggs, milk, strawberries, food additives (tartrazine, benzoates, sulfites)

c) Pharmacological management of this patient (2 marks)

• Immediately stop the causative antibiotic

• Second-generation (non-sedating) H1 antihistamine as first-line:
  • Cetirizine 10 mg orally once daily, OR
  • Loratadine 10 mg orally once daily, OR
  • Fexofenadine 180 mg orally once daily
• Classic (sedating) H1 antihistamine (e.g., Chlorphenamine 4 mg three times daily, Hydroxyzine 25 mg) - alternative, especially useful if pruritus disturbs sleep

• Prednisolone 30-50 mg orally (or IV Hydrocortisone 100-200 mg) - short course (3-5 days) for severe/extensive urticaria with angioedema

• Epinephrine (Adrenaline) 0.5 mg (0.5 mL of 1:1000) IM (thigh/deltoid) - the treatment of choice for anaphylaxis/severe angioedema threatening the airway

Summary Table