Background Adenoid cystic carcinoma is an uncommon malignant neoplasm of salivary glands. We present a case of sublingual gland adenoid cystic carcinoma presenting with trigeminal and hypoglossal neuropathies in a patient with probable benign multiple sclerosis.

Case description This 75-year-old woman was referred by her dentist with a six-month history of lower facial numbness (right V3 distribution). Initial MRI brain scan demonstrated multiple periventricular white matter hyperintensities suggestive of demyelination, prompting neurological referral. She reported a remote history of optic neuritis. On examination, she had left optic atrophy, right V3 sensory loss and a right hypoglossal palsy. Repeat MRI showed subtle high signal and abnormal enhancement of right CN V at the foramen ovale and an enhancing lesion in right sublingual space. Oral examination revealed a small, palpable mass in the floor of the mouth. Biopsy confirmed an adenoid cystic carcinoma of the right sublingual gland with perineural invasion. She was referred for surgical resection and adjuvant radiotherapy.

Discussion This case illustrates: the risk of incorrectly ascribing new neurological symptoms to a known chronic neurological disorder; the value of careful clinical examination in such cases; and the importance of ‘thinking peripherally’ when assessing a patient with cranial neuropathies.