Isolated Paramedian Pontine Reticular Formation (PPRF) syndrome in AQP4 antibody–positive neuromyelitis optica spectrum disorder: a case report

BACKGROUND: Paramedian pontine reticular formation (PPRF) syndrome is characterized by horizontal gaze palsy due to lesions in the PPRF or the abducens nucleus. It is relatively rare and is typically associated with medial longitudinal fasciculus (MLF) syndrome. CASE PRESENTATION: A 53-year-old Japanese woman presented with right lateral gaze palsy and facial nerve palsy, with preserved convergence and left lateral gaze. Neurological evaluation confirmed PPRF syndrome and facial nerve palsy, with no involvement of the MLF. Brain MRI showed a lesion in the right dorsal pons, affecting the PPRF, abducens nucleus, and facial nerve. Serum testing revealed positive antinuclear and anti-AQP4 antibodies. The patient responded well to immunotherapy, with substantial clinical and radiological improvements. She was ultimately diagnosed with AQP4 antibody-positive NMOSD. CONCLUSION: This is the first documented case of isolated PPRF syndrome in AQP4 antibody-positive NMOSD. The findings expand the known phenotypic spectrum of NMOSD and highlight the importance of considering NMOSD, with targeted AQP4 antibody testing, in patients presenting with isolated PPRF syndrome.