MRH is characterized by the association of a cutaneous and mucosal eruption with severe arthropathy and other visceral symptoms. The papulonodular lesions range in diameter from a few millimeters to 2 cm and are round, translucent, and yellow-rose or yellow-brown (Figs. 148-10 and 148-11). Grouping of lesions into plaques can give a cobblestone appearance, but lesions are generally scattered and isolated. They do not tend to ulcerate and are pruritic in about one-third of cases. These lesions preferentially affect the fingers (see Fig. 148-10), the palms and backs of the hands, the juxta-articular regions of the limbs, and the head (see Fig. 148-11). Small, scattered lesions may be found on the trunk. Periungual papules (see Fig. 148-10), arranged around the nail folds, resemble “coral beads” and have been noted in approximately 40% of cases. Severe involvement of the face may lead to a leonine facies. Xanthomatous lesions are found in 30% of cases. Periarticular nodules, resembling rheumatoid nodules, may occasionally be seen. Erythematous, photodistributed macules and papules have been observed in approximately 15% of cases and may be confused with dermatomyositis. Nail changes, including brittleness, longitudinal ridging, and atrophy, may occur. Almost 50% of affected patients have specific nodular lesions of the oral, nasal, and pharyngeal mucosae.
Two different subtypes without joint or visceral manifestations have been described: (1) solitary cutaneous reticulohistiocytosis (or reticulohistiocytoma cutis) and (2) diffuse cutaneous reticulohistiocytosis. Solitary cutaneous reticulohistiocytosis is characterized by a single firm, rapidly growing nodule varying in color from yellow-brown to dark red (Fig. 148-12). Its most common location is the head, but it may be found in almost any cutaneous site. It occurs without evidence of systemic involvement, and its onset may be preceded by trauma. Diffuse cutaneous reticulohistiocytosis is a purely cutaneous form characterized by the eruption of firm, smooth, asymptomatic papulonodular lesions, 3–10 mm in diameter, scattered diffusely over the skin. The color of early lesions is pinkish yellow, whereas older lesions show a red–brown color.
In MRH, severe chronic diffuse polyarthritis with arthralgias is the initial sign of the disease in up to two-thirds of cases. The lesions symmetrically involve the hands (80% of cases), knees (70%), wrists (65%), and less frequently the shoulders, ankles, elbows, hips, feet, and spine. The osteoarticular lesions show a progressive destructive course for 6–8 years and then become stable. Involvement of the muscles (myositis, myotonia, and myoatrophy), cardiopulmonary system (pericarditis, cardiac insufficiency, pleuritis, pulmonary infiltration), eyes (exophthalmos, conjunctival infiltration), gastrointestinal system (gastric ulcer), thyroid gland (thyroid nodules), and submandibular salivary glands have occasionally been reported, but histologic documentation of involvement at these sites is rare. Fever, weight loss, and weakness can be present. The term familial histiocytic dermatoarthritis is used to indicate a particular form of MRH characterized by familial occurrence and typical ocular involvement (glaucoma, uveitis, and cataracts). Internal malignancy may be associated in 15%–27% of cases. Solid tumors such as bronchial, breast, gastric, and cervical carcinomas are most common. Lymphomas and myelodysplastic syndromes have been found less frequently, and malignant melanoma has been reported in three cases. Whether MRH can be interpreted as a true paraneoplastic disease is not clear. Whatever the nature of the association, the incidence of internal neoplasia is such that patients who come for treatment of MRH should be investigated for concomitant internal neoplasm. MRH has been described in association with autoimmune diseases, systemic vasculitis, tuberous sclerosis, sclerosing lesions of the leg, and tuberculosis.