Thickening of the basement membrane as a diagnostic sign of mycosis fungoides

The epidermal basement membrane (BM) is readily identified on skin biopsy specimens stained with periodic acid‐Schiff (PAS) and PAS with diastase (PAS‐D). Thickening of BM can be evidenced in several inflammatory and tumoral conditions. We noticed that most of our biopsy specimens of mycosis fungoides (MF) showed thickening of the BM. We decided to retrospectively study BM thickness in 27 biopsy specimens of MF and compare them with 27 cutaneous biopsy specimens of inflammatory diseases. We studied PAS and PAS‐D stains in all cases and we measured BM thickness with an ocular micrometer. Cases were scored in a four‐tiered system: 0: no detectable staining; 1+ (mild: 9 μm). The difference between both groups (MF vs controls) was highly significant for BM thickness values by both one‐ and two‐tailed t tests (P