Dermatopathology Subspecialty
Reading the slide
Dermatopathology questions test pattern recognition at low and high power. Start with architecture: is the process epidermal, dermal, or both? Is it lichenoid, spongiotic, psoriasiform, interface, or granulomatous? Then assess cytology: atypical melanocytes, lymphocytes, histiocytes, or eosinophils.
High-yield patterns
Lichenoid dermatitis shows band-like lymphocytic infiltrate with basal vacuolar change (lichen planus, lichenoid drug). Spongiotic dermatitis shows intercellular edema with eosinophils (allergic contact). Psoriasiform shows regular acanthosis with parakeratosis and Munro microabscesses. Interface dermatitis with dyskeratosis suggests lupus or erythema multiforme. Granulomatous inflammation suggests sarcoidosis, infection, or foreign body.
Melanocytic lesions
Know the criteria separating benign nevus from melanoma: symmetry, circumscription, maturation with depth, and cytologic atypia. Breslow thickness, ulceration, and mitotic rate drive staging. Immunohistochemistry (S100, SOX10, Melan-A) confirms melanocytic lineage; Ki-67 and HMB-45 help assess proliferation and maturation.
Traps
Questions swap spongiotic and lichenoid patterns, or present a "benign" nevus with one atypical feature to test whether you overcall. Another trap: confusing parakeratosis (retained nuclei) with orthokeratosis.
Rule of thumb
If eosinophils are prominent, think allergic/contact or drug; if plasma cells dominate, think infection, syphilis, or mucosal site; if neutrophils fill the stratum corneum, think psoriasis or dermatophyte.
Worked example
A biopsy with band-like lymphocytes, basal vacuolar change, and Civatte bodies: lichen planus. If the same pattern includes eosinophils and a drug history, lichenoid drug eruption is favored.