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Case Reports

Abstract

Small fiber neuropathy (SFN) is a known cause of hypohidrosis and is diagnosed by specialized epidermal nerve fiber density (ENFD) testing, as standard hematoxylin and eosin (H&E) staining is usually unremarkable. Here we present a case of a 42-year-old woman with a one-year history of generalized hypohidrosis. Biopsies of clinically normal skin were performed for both H&E and EFND evaluation. H&E showed aggregates of PAS-positive material within the coiled and straight eccrine ducts. Congo red staining was negative, and the eccrine units were otherwise histologically normal. ENFD testing revealed markedly reduced nerve density, supporting a diagnosis of SFN. While aggregates of PAS-positive material in eccrine units have been reported following intense sweating and in conditions such as miliaria, they have not been described in patients with SFN-induced hypohidrosis. In prior studies of hyperhidrosis, this material was hypothesized to derive from dark secretory granules in eccrine coils, although newer data suggest that it may represent extracellular polysaccharide substance produced by some strains of Staphylococcal epidermidis. We postulate that impaired innervation of myoepithelial cells surrounding the eccrine unit due to SFN in this patient led to stagnation of sweat flow through the eccrine unit, resulting in the observed intraluminal aggregates. If replicated in other patients with SFN-induced hypo- or anihidrosis, this histologic finding may offer a novel diagnostic clue to SFN on routine H&E staining. Larger-scale studies evaluating skin biopsies from patients with SFN-induced hypohidrosis could help determine the reproducibility and diagnostic utility of the observed findings.