The thickened skin with papules and plaques of a patient with papular mucinosis is explained by focal accumulations of hyaluronic acid and fibroblastic proliferation in the dermis. Findings from protein analysis demonstrated an associated aberration in protein production that appears to be characteristic of this disease: an abnormal peak in the position beyond that of γ-globulin on serum protein electrophoresis and immunologic studies which shows the γ-globulin to be IgG with only L type light chains. The etiology is unknown, but the condition may represent an immunologic response to an unknown antigenic stimulus.
Shapiro CM, Fretzin D, Norris S. Papular Mucinosis. JAMA. 1970;214(11):2052–2054. doi:10.1001/jama.1970.03180110060017