Opsoclonus-Myoclonus Syndrome: Causes and Clinical Features
Opsoclonus-myoclonus syndrome (OMS) is a rare immune-mediated disorder characterized by the clinical triad of chaotic saccadic eye movements (opsoclonus), myoclonus, and ataxia, with additional features of encephalopathy and behavioral disturbances. 1
Clinical Features
The core clinical presentation includes:
- Opsoclonus: Chaotic, involuntary, arrhythmic, conjugate saccadic eye movements that are the hallmark of this syndrome 1, 2
- Myoclonus: Involuntary muscle jerks affecting multiple body regions 1
- Ataxia: Cerebellar dysfunction causing trunk ataxia and coordination difficulties, often severe enough to prevent independent ambulation 3, 4
- Encephalopathy: Altered consciousness, cognitive impairment, and developmental plateauing in children 1, 3
- Behavioral disturbances: Irritability, insomnia, anxiety, and psychoemotional changes 3, 5
Age-Specific Presentations
In children and infants, OMS typically presents in previously healthy toddlers with the full triad plus developmental regression and severe irritability 3. The acute disease may remit, but children are frequently left with persistent cognitive and neurological deficits even after treatment 1.
In adults, the presentation differs by etiology. Idiopathic adult-onset OMS occurs frequently in women, follows a monophasic course, and responds well to intravenous immunoglobulins or corticosteroids 1. The paraneoplastic form affects older women more commonly 1.
Causes
Paraneoplastic Etiologies
In children (approximately 50% of cases): Neuroblastoma is the most common associated malignancy 1, 3. The syndrome develops as an autoimmune response to the tumor, and surgical removal combined with immunotherapy is essential 6.
In adults: The paraneoplastic form is associated with:
Non-Paraneoplastic Etiologies
- Parainfectious/Post-infectious: Viral infections including rotavirus 4, scrub typhus 2, and other viral triggers can precipitate OMS through immune-mediated mechanisms
- Toxic: Organophosphate poisoning 2 and cocaine exposure are documented causes
- Idiopathic: Many cases, particularly in young adult women, have no identifiable trigger but are presumed autoimmune 1, 5
Diagnostic Considerations
Critical Pitfall: Diagnostic Delay
The most common diagnostic error is misdiagnosing OMS as acute cerebellar ataxia, acute disseminated encephalomyelitis, or acute cerebellitis 7. This occurs because opsoclonus may develop later in the disease course—appearing at a median of 96 days in delayed-diagnosis cases versus 11.5 days in early-diagnosis cases 7.
Essential Workup
When OMS is suspected, immediately pursue:
- Tumor screening: Comprehensive imaging (CT chest/abdomen/pelvis, MIBG scan) is mandatory to exclude neuroblastoma in children and breast/lung cancer in adults 1, 3
- CSF analysis: Pleocytosis is common, though MRI is frequently non-informative 1, 4
- Serum and urine studies: Include catecholamines for neuroblastoma screening 3
- Toxicology screening: Serum cholinesterase if organophosphate exposure is possible 2
Antibody Testing
While various neuronal surface antibodies have been investigated, no diagnostic immunological marker has been definitively identified for OMS 5. Some evidence suggests antibodies capable of inducing neuroblastoma cell apoptosis in children, but this is not clinically validated 1.
Prognosis and Long-term Outcomes
Children historically have poor long-term outcomes with residual neurologic and neuropsychiatric sequelae being typical 1, 3. However, more recent combined immunotherapy regimens offer hope for improved outcomes 3.
Adults with idiopathic OMS generally have better prognosis with monophasic courses, while paraneoplastic cases depend on tumor treatment success 1, 5. Relapses can occur in 20-25% of non-paraneoplastic patients, sometimes separated by months or years 1.
The key to minimizing morbidity is early recognition—particularly identifying opsoclonus in any patient with prolonged or relapsing ataxia—and immediate initiation of immunotherapy while pursuing malignancy workup 7.