A rare case of unilateral Cogan's anterior internuclear ophthalmoplegia, upgaze palsy and ataxia caused by dorsal tegmentum lesion at pontomesencephalic junction.

BACKGROUND Cogan's anterior internuclear ophthalmoplegia (INO) is characterized by INO with inability to converge and commonly thought to be due to rostral midbrain lesion. A lesion outside midbrain that causes unilateral Cogan's anterior INO combined with upgaze palsy and ataxia are rarely described. CASE PRESENTATION A 67-year old male presented with left Cogan's anterior internuclear ophthalmoplegia (INO), left appendicular ataxia and bilateral upgaze palsy. A Magnetic Resonance Imaging (MRI) and Magnetic Resonance Angiography (MRA) brain showed a left dorsal tegmental infarct at the level of pontomesencephalic junction. CONCLUSIONS This case highlights the clinical importance of Cogan's anterior INO in combination with upgaze palsy and ataxia, and report possible site of lesion in patients with such constellation. Clinicians should consider looking for cerebellar signs in cases of Cogan's anterior INO, apart from just considering localizing the lesion at the midbrain.