BACKGROUND: Isolated unilateral hypoglossal nerve injury is extremely rare. It may be caused by radiation therapy targeting neoplasms of the cephalic region.

CASE REPORT: A 51-year-old man with synovial sarcoma of the left upper arm status post extensive radiation therapy in 1980 presented in late 2014 with gradual onset of speech difficulty and difficulty moving his tongue for a couple of weeks. Neurological examination revealed isolated left-sided unilateral tongue atrophy. Postradiation residual extensive cicatrix with erythema over the whole left upper extremity extending to the neck on the affected side was noticed. On head magnetic resonance imaging (MRI) before and after administration of gadolinium, he was found to have asymmetrically fatty striations, atrophy, and fibrosis in the left tongue consistent with radiation toxicity. The patient’s tongue weakness persisted without improvement.

CONCLUSIONS: The diagnosis of unilateral hypoglossal nerve injury is usually difficult. Detailed neurological examinations and thorough investigations including head MRI are very helpful. Previous exposure to radiation therapy is a potential cause of hypoglossal nerve injury. To our knowledge, this is the first case report that presents isolated unilateral tongue atrophy as a late complication of juxta cephalic radiation therapy.

Keywords: Atrophy, Arm, Diagnosis, Differential, Follow-Up Studies, Hypoglossal Nerve - radiation effects, Magnetic Resonance Imaging, Radiation Injuries - complications, Sarcoma, Synovial - radiotherapy, Time Factors, Tongue - radiation effects, Tongue Diseases - etiology