Lichen myxedematosus (papular mucinosis): new concepts and perspectives for an old disease.

Lichen myxedematosus (LM) is an idiopathic cutaneous mucinosis; its classification dates back to 1953, when Montgomery and Underwood distinguished 4 types of LM. In the literature, the terms LM, papular mucinosis, and scleromyxedema often have been used indiscriminately as synonyms, but most reported cases of LM or papular mucinosis without indication of the subtype appear in fact to be cases of scleromyxedema. Actually, LM includes 2 clinicopathologic subsets: a generalized papular and sclerodermoid form (the only one which should be called scleromyxedema) with systemic, even lethal, manifestations and a localized form, which does not run a disabling course. The localized form is subdivided into 4 subtypes: (1) a discrete papular form involving any site; (2) acral persistent papular mucinosis involving only the extensor surface of the hands and wrists; (3) papular mucinosis of infancy, a pediatric variant of the discrete form or the acral form of persistent papular mucinosis; and (4) nodular form. A third group of atypical or intermediate forms, not meeting the criteria for either scleromyxedema or the localized form, includes cases of (1) scleromyxedema without monoclonal gammopathy, (2) localized forms with monoclonal gammopathy and/or systemic symptoms, (3) localized forms with mixed features of the subtypes, and (4) not well-specified cases.