Multicentric Reticulohistiocytosis

A rare non-Langerhans cell histiocytosis characterized by the association of specific nodular skin lesions and destructive arthritis.

Epidemiology

Prevalence is unknown but around 200 cases have been reported in the literature so far.

Clinical description

Onset is insidious, usually occurring at around 50 years of age. Multicentric reticulohistiocytosis (MRH) is a progressive disease, articular inflammation becomes more severe and, after periods of worsening and improving symptoms, incapacitating arthritis is a frequent feature. Multiple joints may be involved (mainly of the hands, wrists, shoulders, knees, hips and ankles). Joint symptoms oscillate and severe deforming arthritis, known as mutilating arthritis, is a prominent manifestation in between 11 and 45% of the cases, depending on the patient series. Similarly, cutaneous nodules appear and regress, with new eruptions developing over periods of many months, as the old ones become inactive, stabilize or disappear. The cutaneous nodules are either skin-colored or have a red/brown appearance and are usually asymptomatic. They are more frequent on the upper body, particularly the hands, and may also appear on mucosal surfaces. Internal organ involvement has also been reported. After a period of many years (usually 6 to 8), in the majority of cases, arthritis becomes quiescent and the mucocutaneous nodules stabilize or become smaller.

Etiology

The etiology is unknown. MRH is believed to reflect a peculiar type of reactive inflammatory response to unknown stimuli with involvement of macrophages and T lymphocytes. An underlying malignancy has been described in around a quarter of patients.

Diagnostic methods

Histopathological and immunohistochemical studies (revealing the characteristic reticulohistiocytic granulomas mainly composed of CD68 positive cells) are diagnostic in most cases. Radiologic examinations should be performed in all patients.

Differential diagnosis

The differential diagnosis should include leprosy, rheumatoid arthritis, xanthogranulomas, lymphomas, sarcoidosis, Urbach-Wiethe disease, Farber disease and dermatomyositis (see these terms).

Management and treatment

At present, no satisfactory treatment is available. Some chemotherapeutical schemes, particularly those involving alkylating agents and specific therapies targeted towards the tumor necrosis factor (TNF) or its receptors may lead to some improvement. Systemic steroids are usually of only limited benefit.

Prognosis

Patients with MRH usually undergo spontaneous remission within a variable period of 6 to 8 years, however, sequelae (esthetic sequelae associated with the skin lesions and deforming sequelae associated with the arthritis) are frequent after cure. Death can occur due to internal organ involvement or as a result of the underlying malignancy.