NAIL MATRIX HYPERGRANULOSIS

Nail pathology shares some common features with skin pathology, but it also has its own peculiar aspects. The anatomical and physiological c haracteristics of the nail unit probably play a major role in determin ing these pathological differences. Although the presence of keratohya line granules is a normal feature of the skin, there is no granular la yer in the normal nail matrix. As a consequence, nail matrix hypergran ulosis should be considered a separate entity from skin hypergranulosi s. In our review of 150 longitudinal nail biopsy specimens, keratohyal inee granules were seen in the nail matrix of 24 cases of lichen planu s, 29 cases of spongiotic trachyonychia, 10 cases of psoriasis, and th ree cases of Hallopeau acrodermatitis. In all cases, the presence of k eratohyaline granules was associated with the absence of the normal ke ratogenous zone. Similar nail matrix features were detectable in three cases of malignant melanoma, two cases of primary systemic amyloidosi s, and one case of histiocytoid hemangioma compressing the nail matrix . Our data suggest that inflammatory and compressive insults to the na il matrix cause both disappearance of the keratogenous zone and matrix keratinization with the formation of keratohyaline granules. Skin hyp ergranulosis reflects a hyperplasia of a normal skin component. In the nail matrix, however, hypergranulosis represents the appearance of st ructures not normally present. Nail matrix hypergranulosis should be c onsidered a pattern of nail matrix reaction to different inflammatory insults. It is therefore more analogous to epidermal parakeratosis tha n to epidermal hypergranulosis.