Left shoulder pain from humeral Rosai-Dorfman disease.

Rotator cuff impingement was suspected when a 23-year-old male police officer presented to the orthopedic clinic with gradual-onset left shoulder pain and weakness; however, conservative management did not improve the patient's symptoms. Subsequent imaging revealed a lytic lesion in the left humeral head, with CT-guided biopsy findings consistent with Rosai-Dorfman disease, an extremely rare histiocytic disorder. Typically self-limiting and benign, Rosai-Dorfman disease is characterized by overproduction and accumulation of rare non-Langerhans cell histiocytes, a type of immune cell, in various tissues. These histiocytes most commonly proliferate in the lymph nodes, causing hallmark lymph node enlargement. In cases that do not spontaneously resolve, individualized treatment may be required. The patient in this case report returned to normal activity following improvement without intervention.