Dermatology for Final MB: Student Prep Guide

Specialty Postings · Dermatology Prep Guide

High-yield revision, histological exceptions to memorise cold, clinical comparison tables, and 12 self-test questions distilled for the Final MB;BS clinical examinations.

1. Core Topic Checklist

Ensure you can confidently define and explain each curriculum topic without notes:

Skin embryology & epidermal layers (including the stratum lucidum exception)

Eczema: diagnostic presentation, spongiosis, and cellular infiltration

Acne vulgaris: comedones, Cutibacterium acnes, and keloid as a complication

Psoriasis vs. Lichen Planus: Koebner phenomenon, parakeratosis, Munro abscesses

Lichen planus: the 5 P's, band-like infiltrate, and oral involvement

Stevens-Johnson Syndrome: drug triggers, SCORTEN prognostic criteria, and care

Pigmentary disorders: Vitiligo (PUVA) vs. Albinism (sun protection & SCC risk)

Scabies: Sarcoptes scabiei, nocturnal pruritus, permethrin, Norwegian crusted type

Fungal infections: Tinea corporis/manuum, and Tinea capitis non-scarring alopecia

Bullous disorders: Subepidermal Pemphigoid vs. Intraepidermal Pemphigus (desmogleins)

Topical steroids: fluorinated potencies, skin atrophy, and dyschromia side effects

Dermatology history-taking: familial clustering, first anatomical lesion, sun exposure

2. Core Clinical Summaries

2.1 Psoriasis vs. Lichen Planus Comparison

Diagnostic Feature	Psoriasis	Lichen Planus
Clinical Lesions	Well-demarcated erythematous plaques with silvery-white micaceous scales	The 5 P's: Purple, Pruritic, Polygonal, Planar, Papules/Plaques; Wickham striae
Koebner Phenomenon	Present (lesions along trauma lines)	Present (isomorphic response)
Parakeratosis	Present (retained nuclei in corneum)	Absent (Orthokeratosis present)
Munro Microabscesses	Present (sterile neutrophils in stratum corneum)	Absent
Dermal Infiltrate	Perivascular lymphocytic infiltrate	Dense band-like (lichenoid) lymphocytic infiltrate at dermo-epidermal junction
Congenital State	Not congenital (polygenic predisposition)	Cell-mediated autoimmune disease; not congenital

2.2 Bullous Disorders: Anatomical Cleavage Levels

Bullous Disease	Level of Cleavage	Pathogenesis & Clinical Features
Bullous Pemphigoid	Subepidermal	Autoantibodies against hemidesmosomal antigens (BP180/BP230); tense, non-fragile bullae; negative Nikolsky sign; elderly patients.
Pemphigus Vulgaris	Intraepidermal (Suprabasal)	Autoantibodies against desmoglein 3 (& 1); acantholysis; flaccid fragile blisters that rupture leaving erosions; positive Nikolsky sign; oral mucosal involvement.
Epidermolysis Bullosa	Dermo-epidermal junction / Dermis	Inherited mechanobullous fragility disorder; mechanical shearing triggers blister formation.

2.3 Stevens-Johnson Syndrome (SJS / TEN)

Severe immune-complex-mediated mucocutaneous adverse drug reaction resulting in full-thickness epidermal necrosis.

Key Triggering Drugs:Sulfonamides (cotrimoxazole), antiepileptics (carbamazepine, phenytoin, phenobarbital), allopurinol, NSAIDs. Chloroquine is a documented but rare cause.

SCORTEN Poor Prognostic Factors:Age ≥40 years, associated malignancy, heart rate ≥120 bpm, epidermal detachment >10% BSA, serum urea >10 mmol/L, serum glucose >14 mmol/L, bicarbonate <20 mmol/L.

3. “Which is NOT...” High-Yield Exceptions

Examiners deliberately formulate MCQ and viva questions targeting the item that does not belong:

Examiner Stem Question	The Correct Exception to Select
Which structure is NOT an ectodermal skin derivative?	The Dermis (derived from embryonic mesoderm).
Which epidermal layer is NOT universally present?	Stratum Lucidum (found exclusively in thick glabrous skin of palms & soles).
Which is NOT a morphological primary lesion of acne?	Keloid (keloid is a secondary complication/scarring, NOT a primary lesion).
Which is NOT a member of the papulosquamous group?	Vitiligo (an autoimmune pigmentary depigmentation disorder).
Which histological feature is ABSENT in lichen planus?	Parakeratosis and Munro microabscesses (hallmarks of psoriasis, not LP).
Is psoriasis a congenital disorder?	No. Psoriasis is an acquired immunogenetic inflammatory disorder.

4. 12 High-Yield Self-Test Questions with Model Answers

1. Name the embryonic germ layer origin of the epidermis.

Answer: Ectoderm (the underlying dermis originates from mesoderm).

2. Which epidermal histological layer is confined strictly to thick palmar and plantar skin?

Answer: Stratum lucidum (situated between stratum granulosum and stratum corneum).

3. Enumerate the primary morphological lesions of acne vulgaris.

Answer: Comedones (open/blackheads, closed/whiteheads), inflammatory papules, pustules, and nodules.

4. Is a keloid classified as a morphological lesion of acne vulgaris?

Answer: No. A keloid is a secondary complication of defective cicatrization, not a lesion type.

5. Name two hallmark histological features found in psoriasis that are absent in lichen planus.

Answer: Parakeratosis (nuclei retention in keratin layer) and Munro microabscesses (neutrophilic collections).

6. Define the Koebner isomorphic phenomenon.

Answer: The development of typical disease lesions along lines of cutaneous mechanical trauma or excoriation.

7. State two validated poor prognostic factors in Stevens-Johnson syndrome (SCORTEN).

Answer: Age ≥40 years, coexisting malignancy, tachycardia ≥120 bpm, serum urea >10 mmol/L, or hyperglycemia.

8. Identify the causative microscopic organism of human scabies.

Answer: Sarcoptes scabiei var. hominis.

9. Which dermatophyte infection classically causes non-scarring alopecia in paediatric patients?

Answer: Tinea capitis (hair regrowth occurs following successful systemic antifungal therapy).

10. At what microscopic anatomical planes do cleavage occur in bullous pemphigoid vs. pemphigus vulgaris?

Answer: Subepidermal in bullous pemphigoid; Intraepidermal (suprabasal acantholytic) in pemphigus vulgaris.

11. What is the single most vital counseling instruction for a patient diagnosed with oculocutaneous albinism?

Answer: Strict lifelong photoprotection: broad-spectrum sunscreen (SPF ≥50), UV-protective clothing, wide-brimmed hats to prevent squamous cell carcinoma.

12. List three cutaneous adverse effects of chronic potent topical corticosteroid application.

Answer: Epidermal atrophy (paper-thin skin), striae distensae, telangiectasia, easy purpura/bruising, steroid acne, and dyschromia.

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