Parakeratosis is defined as:

Retention of nuclei in stratum corneum

Decreased thickness of stratum corneum

Retention of cytoplasmic contents in stratum corneum

Increased thickness in stratum corneum

A 74-year-old woman has noted increasing size and number of darker brown patches on the dorsum of each hand for the past 15 years. They do not change with sun exposure, are nonpruritic, and non-tender. On examination, these 0.5- to 1-cm lightly pigmented lesions are flat. Which of the following is the most likely microscopic finding in these lesions?

Loss of melanin in surrounding skin

Which of the following is NOT true about dysplastic nevus syndrome?

It is inherited in an autosomal recessive pattern.

Approximately half of such patients develop melanoma by age 60.

It is associated with mutations in BRAF and NRAS.

It is a disorder characterized by numerous dysplastic nevi.

Inflammatory Dermatoses for UPSC-CMS: High-Yield Pathology Lessons

Eczematous Dermatoses - Itch & Scratch Saga

General: Pruritus, erythema, vesicles (acute); scaling, lichenification (chronic).
Histopathology:
- Acute: Spongiosis (intraepidermal edema), lymphocytic infiltrate.
- Chronic: Acanthosis, hyperkeratosis, parakeratosis.

⭐ Spongiosis is the hallmark of acute eczematous dermatitis.

Atopic Dermatitis (AD):
- Patho: Th2 immune response, filaggrin (FLG) gene mutations.
- Distribution: Infants (face, extensors); Children/Adults (flexures).
Allergic Contact Dermatitis (ACD):
- Patho: Type IV (delayed) hypersensitivity. Haptens (e.g., nickel, poison ivy).
- Morph: Well-demarcated lesions at contact site.
Irritant Contact Dermatitis (ICD):
- Patho: Non-immunologic, direct chemical injury to keratinocytes.
- Morph: Burning, stinging > itch. Often hands.
Seborrheic Dermatitis (SD):
- Patho: Malassezia spp. role, inflammation.
- Distribution: Scalp (dandruff), face (nasolabial folds, eyebrows), chest. Greasy yellow scales.

Papulosquamous Disorders - Scaly Skin Stories

Psoriasis vs. Lichen Planus

Feature	Psoriasis	Lichen Planus
Clinical	Well-demarcated erythematous plaques, silvery scales. Auspitz sign, Koebner phenomenon. Guttate: drop-like, post-strep.	📌 5 P's: Purple, Pruritic, Polygonal, Papules, Plaques. Wickham's striae (lacy white lines). Flexor surfaces, oral/mucosal.
Histology	Parakeratosis, Munro's microabscesses (neutrophils in S. corneum), acanthosis with clubbed rete ridges, suprapapillary thinning.	Hyperkeratosis, sawtooth rete ridges, band-like lymphocytic infiltrate at DEJ, Civatte bodies (apoptotic keratinocytes).

Histology of Psoriasis and Lichen Planus

Vesiculobullous Diseases - Bubble Trouble Tales

Autoimmune blistering disorders. Key distinction: level of epidermal split.

Feature	Pemphigus Vulgaris (PV)	Bullous Pemphigoid (BP)
Pathogenesis	AutoAbs vs. Desmoglein 1 & 3 (intercellular)	AutoAbs vs. BPAG1 (BP230) & BPAG2 (BP180) (hemidesmosomes)
Level of Split	Intraepidermal (suprabasal acantholysis)	Subepidermal (dermo-epidermal junction)
Clinical: Bullae	Flaccid, easily ruptured, painful erosions	Tense, intact, often pruritic
Nikolsky Sign	Positive (+) (pressure extends blister)	Negative (-)
Mucosal Involvement	Common, severe (oral >50%)	Less common (~10-30%), milder
Age (Typical)	40-60 years	>60 years (elderly)
Direct IF (DIF)	Intercellular IgG/C3 ("Fishnet" pattern)	Linear IgG/C3 at Basement Membrane Zone (BMZ)

⭐ Pemphigus vulgaris shows intraepidermal acantholysis and a 'row of tombstones' (basal cells attached to dermis) appearance on histology.

Hypersensitivity Reactions - Rash Decisions Drama

Spectrum of severe mucocutaneous reactions: EM Minor → EM Major → SJS → SJS/TEN Overlap → TEN.
Triggers:
- EM: Infections (📌 HSV most common), Mycoplasma.
- SJS/TEN: Drugs (e.g., sulfonamides, allopurinol, anticonvulsants, NSAIDs), Mycoplasma, vaccines.
Key Features:
- EM: Target/iris lesions (often acral). EM Minor: minimal/no mucosal. EM Major: mucosal involvement (≥1 site), <10% BSA.
- SJS/TEN: Prodrome (fever, malaise), painful atypical targets/macules → widespread blistering, Nikolsky sign (+), severe mucosal erosions (≥2 sites).
Histology:
- EM: Keratinocyte apoptosis, vacuolar interface change, lymphocytic infiltrate.
- SJS/TEN: Full-thickness epidermal necrosis, subepidermal split/blisters.
BSA Detachment for SJS/TEN Classification:
- SJS: <10%
- SJS/TEN Overlap: 10-30%
- TEN: >30% (SCORTEN score for prognosis)

⭐ Herpes simplex virus is the most common trigger for Erythema Multiforme.

Severe mucosal erosions in Stevens-Johnson syndrome

High‑Yield Points - ⚡ Biggest Takeaways

Psoriasis: Characterized by acanthosis, parakeratosis, Munro's microabscesses, and elongated rete ridges.

Lichen Planus: Features sawtooth rete ridges, Civatte bodies, and a dense band-like lymphocytic infiltrate at the dermo-epidermal junction.

Eczema (Dermatitis): Acute shows spongiosis; chronic presents with acanthosis and hyperkeratosis.

Pemphigus Vulgaris: Intraepidermal bullae due to acantholysis (Nikolsky sign positive); antibodies target desmogleins.

Bullous Pemphigoid: Subepidermal bullae with numerous eosinophils (Nikolsky sign negative); targets hemidesmosomal proteins.

Dermatitis Herpetiformis: Subepidermal bullae with neutrophilic microabscesses at dermal papillae tips; strong celiac disease association with IgA deposits.

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