Consequences of Misdiagnosed Opsoclonus Myoclonus Ataxia Syndrome (OMAS)

OBJECTIVES: To evaluate the impact of misdiagnosis on patients with OMAS, we assessed time to, and disease severity at, OMAS diagnosis for patients initially misdiagnosed v. correctly diagnosed.

METHODS: OMAS Natural History Registry: demographics, family history, disease, and treatment data input by the patient and/or caregiver. Study Population: 122 patients with demographic, family history, disease information. Statistics: Pearson χ², Fisher’s exact (categorical), z-test (proportions), Mann-Whitney U (continuous), Shapiro-Wilk (normality). Matched pairs by exact propensity score matching (PSM) without replacement.

RESULTS: Most (60%) study patients were initially misdiagnosed; this group had a higher proportion of family history autoimmune disease (40% v. 20% correctly diagnosed, p=0.025) and lower proportions of onset by age 3 (82% v. 96% correctly diagnosed, p=0.024) and opsoclonus at onset (52% v. 73% correctly diagnosed, p=0.018). Final PSM, based upon opsoclonus, US residence, onset age, and family history autoimmune disease, yielded 31 pairs. Matched cohorts of misdiagnosed v. correctly diagnosed were not significantly different by demographics, symptoms, or family history. Mitchell-Pike severity scores at diagnosis were not significantly different between cohorts in study or matched samples. Misdiagnosed groups had higher proportions with abnormal mood (study: 100% v. 88% correctly diagnosed, p=0.002; matched: 100% v. 84% correctly diagnosed, p=0.053) and impaired speech (study: 85% v. 67% correctly diagnosed, p=0.027; matched: 87% v. 68% correctly diagnosed, p=0.127) though significance was not reached in the matched set. Mean (median) months to diagnosis was greater in misdiagnosed groups (study: 5.9 (2.0) v. 2.8 (1.0) correctly diagnosed, p<0.001; matched: 4.7 (2.0) v. 3.2 (1.0) correctly diagnosed, p=0.048).

CONCLUSIONS: In the OMAS Natural History Registry, patients initially misdiagnosed were delayed in receiving the accurate OMAS diagnosis. Impaired speech and abnormal mood were more common in misdiagnosed cohorts, though significance was only achieved in the starting study population. Enrollment into the registry is ongoing.