Optic Nerve Head Melanocytoma Co-existing in a Case of Thyroid Eye Disease: Co-incidence or Cause?

Optic Nerve Head Melanocytoma (ONHM) is a rare benign pigmented tumour of the uveal tract, seen commonly at the optic nerve head. The tumour is associated with a few ocular and systemic conditions. It usually remains stationary and rarely (1-2%) undergoes a malignant transformation. With the progressive understanding of its benign nature with advancing imaging modalities, observation with regular follow-up is the mainstay of treatment. A 35-year-old female, presented with complaints of foreign body sensation in both eyes. She was a known case of graves’ disease under treatment with anti-thyroid drugs and beta blockers. Ocular examination revealed classic signs of thyroid eye disease. The left eye fundus revealed a large, black, globular tumour in the optic nerve head obscuring the entire disc and Ultrasound B scan revealed a tumour at the optic nerve head with high echogenicity. Optical Coherence Tomography (OCT) through the mass revealed a dome-shaped elevation with obscuration of underlying details due to heavy pigmentation, with no signs of subretinal exudation or edema. Thyroid profile was within normal limits. A diagnosis of left eye ONHM was made. The patient was started on tapering doses of systemic steroids and was regularly followed up to monitor the tumour growth for 18 months. This is the first reported case of ONHM co-existing with thyroid eye disease and this association could be coincidental or embryological. This case highlights the need for ophthalmologists to be familiar with this benign condition and for regular careful follow-up of such patients.