Introduction:Opsoclonus Myoclonus Ataxia Syndrome (OMAS) is characterised by opsoclonus, myoclonus, ataxia and behaviour abnormalities.

Methodology: A retrospective review of case records (January 2011 to December 2017) of OMAS presenting to a tertiary care teaching centre in north India was performed.

Results:Overall33 (21 females) cases were identified. The median age of onset and time to diagnosis were 19 (IQR: 17-20)and6 (IQR:4-8)months respectively.

The most common initial presenting features were ataxia (n=13) and behaviour abnormalities(n=11). Overall clinical profile includedataxia (n=33), , opsoclonus (n=30), excessive irritability (n=28) and  myoclonus (n=18).

Twenty-five patients(75%) hadassociated tumour (ganglioneuroblastoma 13 and neuroblastoma 12). Definite prodromal illness in preceding 4 weeks was present in 3 children. Serum antineuronal antibodies were positive in 6 cases (anti-Hu=2 ,anti PNMA2=4).

All patients received ACTH therapy (51%, 17/33, ACTH alone, maximum dose: 60 IU, median duration: 12 (IQR: 07-22) months followed by oral azathioprine). Combination of ACTH and IVIG was used for severe cases (encephalopathic and/or non ambulatory, 48%,16/33). Relapseoccurred in 12 cases (7 tumor positive) with a median time to relapse of 1 (IQR: 0.5-2) monthafter completion of treatment. All relapses were treated with repeat ACTH, rituximab was given to poor responders (3/12; 25%). With a minimumfollow-up of 6 months, 64 % showed normal Pediatric Cerebral Performance Category(PCPC)scores for disability.

Conclusion:OMAS is a potentially catastrophic immune mediated treatable entity. All patients should undergo relevant tumour screening.