Localized papular mucinosis with IgA nephropathy: a case report.

BACKGROUND Papular mucinosis is an idiopathic cutaneous mucinosis. It includes 3 clinicopathologic subsets according to the recent Rongioletti classification: a generalized papular form, a localized form, and atypical forms. The localized form is subdivided into 5 subtypes. The atypical form does not meet the criteria for either the generalized papular form or the localized forms and includes localized forms with monoclonal gammopathy and/or systemic symptoms. OBSERVATIONS We describe a 37-year-old man who had multiple small, waxy papular lesions on the neck for 4 years. One year after the lesions first appeared, he developed IgA nephropathy. No paraproteinemia or thyroid dysfunction was observed. Histologic examination of the skin lesions showed mucin deposits in the upper dermis. Alcian blue-positive mucin was also found in the renal interstitium and around some vessels and capillary loops. A diagnosis of localized papular mucinosis with IgA nephropathy (atypical form) was made after the biopsy. CONCLUSIONS The patient showed an unusual manifestation of localized papular mucinosis with the lesions confined to the neck and IgA nephropathy. Alcian blue staining is a useful way to determine kidney involvement of papular mucinosis.