Isolated rosai-dorfman disease presenting as peripheral mononeuropathy and clinically mimicking a neurogenic tumor: case report

BACKGROUND Rosai-Dorfman disease is a rare idiopathic disorder of proliferative histiocytes affecting the lymph nodes. It usually manifests as bilateral cervical lymphadenopathy and fever with concurrent polyhyperglobulinemia. Cases involving the nervous system are quite rare; most CNS lesions are located intracranially or arise from the spinal dura or leptomeninges. To our knowledge, there has been no previous report of isolated Rosai-Dorfman disease presenting as peripheral mononeuropathy. CASE REPORT We report a 43-year-old female with isolated extranodal Rosai-Dorfman disease in the medial aspect of the right upper arm, which presented as aberrant ulnar neuropathy caused by a mass encasing the right basilic vein and the medial anteriobrachial cutaneous branch of the right ulnar nerve. Preoperative diagnosis was a neurogenic tumor. The patient underwent excision of the mass, and pathologic examination confirmed the diagnosis of Rosai-Dorfman disease. CONCLUSION An unusual case of extranodal isolated Rosai-Dorfman disease, presenting as peripheral mononeuropathy, is reported. Clinically, it simulated a neurogenic tumor, extending the etiologic spectrum of entrapment neuropathy of the peripheral nerve.