Clinical significance of umbilical region involvement in pemphigus vulgaris in a series of 81 ethnic Poles: a comparative analysis of the distribution of lesions in two infrequent locations

Introduction
Autoimmune bullous diseases are potentially life-threatening dermatoses which present with cutaneous and/or mucosal blisters, diagnosed on the basis of clinical manifestations, direct immunofluorescence of perilesional tissue, and serum testing for circulating autoantibodies. Sometimes, lesions in the navel can lead to the diagnosis of a bullous disease. Aims: The aim of this comparative study was to assess the frequency of occurrence of pemphigus lesions located in the navel area and nail apparatus in pemphigus vulgaris (PV) in ethnic Poles.

Material and methods
Eighty one patients (31 males and 50 females, mean age 59 years) with dermatoses of the PV group diagnosed in 2002-2020 were retrospectively analysed using their photographic files. Statistical analysis was performed using the difference test between two proportions to check the difference between the percentage of PV patients with navel area involvement and nail apparatus involvement.

Results
There was no statistically significant difference between PV patients with nail apparatus involvement (12.3%) and navel area involvement (14.8%) (p = 0.4632). Only females had lesions in the navel area in our series of PV patients.

Conclusions
It is speculated that the causal relationship may exist between the female reproductive system and the pattern of expression of PV lesions around the umbilicus. The awareness that PV can infrequently affect the umbilical region and the nail apparatus should help in some cases to establish the diagnosis of PV. The periumbilical involvement can facilitate the performance of DIF in individuals with lesions in less accessible areas.