Multicentric reticulohistiocytosis

Multicentric reticulohistiocytosis (MRH), also known as lipoid dermatoarthritis or reticulohistiocytoma, is a rare systemic disease characterized by the proliferation of histiocytes (a type of immune cell) and multinucleated giant cells in the skin, joints, and other organs. It is classified as a non-Langerhans cell histiocytosis. The disease primarily affects the musculoskeletal system and the skin, though it can also involve mucous membranes, bone, and internal organs. The hallmark clinical features include a destructive, symmetric polyarthritis that can lead to severe joint damage (arthritis mutilans) and characteristic papulonodular skin lesions. The skin nodules are typically reddish-brown to yellow and frequently appear on the hands, face, and ears, with a distinctive "coral bead" appearance around the nail folds. Joint involvement most commonly affects the interphalangeal joints of the hands but can involve any joint. Approximately 25-30% of cases are associated with an underlying malignancy, making cancer screening an important part of the diagnostic workup. Other systemic manifestations may include involvement of the heart, lungs, kidneys, and salivary glands. There is no universally effective treatment for multicentric reticulohistiocytosis. Management strategies include immunosuppressive agents such as methotrexate, cyclophosphamide, and corticosteroids. Biologic therapies, particularly TNF-alpha inhibitors (such as infliximab and etanercept) and bisphosphonates, have shown benefit in some patients. The disease may undergo spontaneous remission after several years, but significant joint destruction can occur before this happens. Early diagnosis and aggressive treatment are important to minimize irreversible joint damage. The condition predominantly affects middle-aged adults, with a female predominance.

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