Trigeminal hypertrophic interstitial neuropathy presenting as unilateral proptosis, ptosis, tearing, and facial neuralgia

Purpose: To show the utility of MRI and histology in diagnosing rare cases of trigeminal hypertrophic interstitial neuropathy (HIN). Observations: A 57-year-old African-American woman presented with a 4-year history of right eye proptosis with tearing, headaches, and worsening right-sided trigeminal neuralgia symptoms and jaw pain. HIV and diabetes tests were negative and thyroid function was normal. MRI identified abnormal thickening of all trigeminal nerve divisions and proptosis secondary to right trigeminal nerve V1 division enlargement. The excised tissue contained S-100 positive Schwann cells in an onion-bulb pattern. Headaches resolved, but proptosis and mild trigeminal neuralgia remained 1 year post-surgery. Conclusions and importance: Trigeminal HIN is very rare, but presents as chronic progressive ocular symptoms with trigeminal neuralgia. Trigeminal nerve hypertrophy is identified by MRI and confirmed histopathologically by detection of Schwann cells in an onion bulb formation.