Update on Multicentric Reticulohistiocytosis Save

Have you ever seen multicentric reticulohistiocytosis (MRH)?  Don't worry, it's a rare non-Langerhans cell histiocytosis condition, characterized by papulonodular skin lesions and symmetric erosive polyarthritis, and has only been described in fewer than 500 cases reported worldwide.

There were 3 recent reports on MRH:

• JAMA Dermatology has described a case of MRH - A man in his 60s presented with a 3-month history of multiple nodules on hands with pain in the shoulders, elbows, metacarpophalangeal, and interphalangeal joints. Other findings included erythema on the face, chest, and back. Hand were swollen, with scattered skin-colored papules and nodules. Labs were negative for RF, but positive for anti–SSA antibodies. After no response to ibuprofen, the patient responded to oral prednisone and increasing doses of methotrexate and did well for 8 years.
• JAK Inhibitors Show Promise in Refractory Multicentric Reticulohistiocytosis: a case series from RMD Open describes three patients with heterogeneous MRH presentations who achieved sustained, multidomain responses to JAK inhibitors. All three developed inflammatory arthritis — ranging from arthralgia to destructive arthropathy — and early cutaneous papules predominating on the face and trunk. Systemic features included digital microangiopathy with a scleroderma-like capillaroscopic pattern in one patient, interstitial lung disease with lymphocytic alveolitis in another, and two patients met criteria for Sjögren's syndrome. Notably, all three were anti-Ro52 positive, underscoring MRH's autoimmune complexity.  The diagnosis was confirmed histologically by CD68+ histiocytic and multinucleated giant cell infiltration. Prior therapies — including conventional DMARDs and TNF inhibitors — were either ineffective or poorly tolerated. Treatment with tofacitinib or upadacitinib produced rapid, durable improvement across articular, cutaneous, vascular, and pulmonary domains.
• Refractory polyarthritis as multicentric reticulohistiocytosis: They describe a patient a 51-year-old man with 6 months of acute inflammatory polyarthralgia, synovitis, and extensor tenosynovitis who later developed multiple papulonodular lesions developed on his hands, face, and auricular regions. A skin biopsy demonstrated CD68-positive histiocytes and multinucleated giant cells with eosinophilic ‘ground-glass’ cytoplasm, confirming multicentric reticulohistiocytosis. Treatment with corticosteroids and methotrexate was ineffective, whereas tumour necrosis factor-alpha inhibitor therapy resulted in meaningful clinical improvement and steroid sparing. Early recognition, imaging, and a biopsy are essential to avoid irreversible joint damage.