METHODS: Histopathology samples of all biopsy-proven FP cases were retrieved from archives and investigated for inflammatory parameters, presence of pagetoid dyskeratosis, as well as CD163, CD10, and CD34 immunostaining pattern of dermal spindle/stellate or multinucleate cells (graded from 0 to 4).
RESULTS: Thirty-two cases of FP were identified. A high rate of inflammatory parameters including interface changes (20/32), spongiosis (31/32), and dermal lymphocytic inflammation (31/32) were detected. Pagetoid dyskeratosis was identified in eight out of 32 cases (25%). A grade 4 staining revealing a strong dendritic pattern was confirmed in all FP cases with CD163 immunohistochemistry including atypical variants such as granular FP, compared with CD10 (11/32) and CD34 (3/32).
CONCLUSIONS: The dendritic cellular proliferation in FP may represent an inflammatory response to various stimuli; pagetoid dyskeratosis is a relatively common and underrecognized epidermal feature and CD163 immunostaining may be used as an adjunctive diagnostic tool in unusual histopathological subtypes.