In The Name Of God Introduction to Dermatopathologic By: Dr Marhamati

Histopathology : gold standard for most dermatologic diagnoses but not all lesions are amenable to definitive (specific) histologic diagnosis. SPECIFICITY = True Negative Rate SENSITIVITY = True Positive Rate

Most melanoma are positive for S100(high sensitivity) All benign melanocytic neoplasms are positive for S100(low specificity) Frequent mitoses are common in bulky melanoma,but rare in most benign melanocytic neoplasms(relatively specific but non pathognomic marker for melanoma) Mitotic figures are absent in most thin nontumorigenic melanoma(low sensitivity) HMB45 antibody found in: Melanoma,blue nevus and other benign lesions

Ultrastructural, immunohistochemical, and molecular test :increased specificity for many diagnoses Immunofluorescence used to differentiate among vesiculobullous disorders. Fusion transctipt for EWS-ATF1 detected by RT-PCR or FISH used to distinguish between primary clear cell sarcoma and a malignant melanoma

Morphology is still the basis of diagnosis for most neoplasms and inflammatory dermatoses. Follow-up studies of outcome: gold standard for validation of diagnostic utility

Histologic picture of many inflammatory dermatoses is more typically “ Compatible with” or suggestive, rather than “Diagnostic of” clinical process. For example: papulosquamous dermatoses, such as psoriasis or lichen planus.

Histopathology can ruling out an important diagnosis( even though an exact diagnosis cannot be made) For example: review of a biopsy of a psoriasiform plaque may rule out mycosis fungoides , but may not be able to establish the specific diagnosis of psoriasis.

Diagnostic limitations of histology in :infectious and neoplastic processes For example, infectious granulomas of different etiologies are not readily distinguishable, unless the causative organism can be demonstrated.(with more sensitive staining for organism as Grocott or acid-fast ) PCR test for foreign DNA diagnostic for infectious agent.

Histology may not suffice to distinguish between keratoacanthoma and SCC, or between Spitz nevus and melanoma Comparative genomic hybridization Or FISH differentiated between spitz nevus and melanoma

Improving diagnostic specificity will be achieved by: Correlation between molecular, histologic, gross anatomic levels with the physical findings and clinical history, interpreted in the context of the whole patient and his or her environment, with long-term follow-up serving as the “Gold standard”. Tumors of uncertain malignant potential tailored with worst- case scenario