Progressive Mucinous Histiocytosis
Key features
Affects primarily women
Usually an autosomal dominant disorder but can be sporadic
Involvement, which is limited to the skin, is chronic and unremitting
Introduction and pathogenesis
Progressive mucinous histiocytosis is an extremely rare form of non-LCH. Most cases are inherited in an autosomal dominant pattern, but rare sporadic cases have also been observed. A germline gain-offunction missense mutation in PDGFRB (platelet-derived growth factor receptor beta) was recently detected in the original pedigree73a.
Epidemiology
Most affected patients are women, but an explanation for this skewing is lacking. To date, eight families with the hereditary form have been described.
Clinical features
Cutaneous lesions appear during childhood or adolescence and persist indefinitely. They consist of multiple, discrete, skin-colored to red– brown papules or nodules that favor the face, hands, forearms, and legs in a symmetric distribution pattern. There is neither mucosal nor visceral involvement and no associated diseases have been described. The clinical course is chronic with no spontaneous remissions.
Pathology
Progressive mucinous histiocytosis is characterized by an accumulation of spindled or epithelioid histiocytes in the upper and mid dermis that is accompanied by mucin deposition. The histiocytes express the phenotype of mature macrophages with positivity for CD68 and CD163.
Differential diagnosis
The differential diagnosis includes other non-LCHs, multinucleated cell angiohistiocytoma, and multiple dermatofibromas. These entities can be distinguished by clinical, histopathologic, and immunohistochemical features.
Treatment
There are no specific treatments. Lesions may be removed by surgery, CO laser, or cryotherapy. Use of PDGFR inhibitors (e.g. imatinib) may represent an additional therapy.