Opsoclonus myoclonus ataxia
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opsoclonus myoclonus ataxia syndrome
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Opsoclonus–Myoclonus–Ataxia Syndrome (OMAS)
Definition
Opsoclonus–myoclonus–ataxia syndrome (OMAS), also called "dancing eyes–dancing feet syndrome," is a paraneoplastic or post-infectious neurological disorder defined by three core features:
- Opsoclonus — involuntary, chaotic, arrhythmic, large-amplitude conjugate saccades occurring in all directions of gaze (not suppressed by fixation)
- Myoclonus — diffuse or focal irregular muscle jerks; may involve head, trunk, or limbs
- Ataxia — truncal or limb incoordination; cerebellar signs including truncal titubation
Additional features commonly accompany the triad: irritability, insomnia, behavioral changes, encephalopathy, and hypotonia (especially in children).
Pathophysiology
The pathologic substrate is not fully established, but current evidence points to disinhibition of the fastigial nucleus of the cerebellum as a core mechanism. Neuropathological findings are relatively mild — cell loss in the Purkinje layer, inferior olives, and brainstem with mild inflammatory changes — disproportionate to the clinical severity.
The syndrome is strongly immune-mediated. Autoimmune responses against a variety of neuronal antigens have been identified:
| Antibody | Associated Tumor |
|---|---|
| Anti-Ri (ANNA-2) | Breast, ovarian, gynecologic cancers |
| Anti-Hu (ANNA-1) | SCLC; ~5% of children with neuroblastoma |
| Glycine receptor (GlyR) | SCLC |
| No antibody detected | Majority of cases |
Importantly, no single opsoclonus-specific antibody has been identified — most patients are seronegative.
Etiology
In Children
- The most common cause is neuroblastoma — at least 50% of pediatric OMAS cases have an underlying neuroblastoma (a neural crest tumor)
- Neurological symptoms precede the tumor diagnosis in ~50% of cases
- Children with neuroblastoma and opsoclonus have a better tumor prognosis than those without opsoclonus
- The next most common etiology is post-infectious / viral (e.g., post-enterovirus, post-EBV)
- If neuroblastoma is suspected, workup includes urine VMA and HVA + MRI/CT of chest and abdomen
In Adults
- Paraneoplastic: SCLC (small cell lung cancer), breast cancer, ovarian cancer, gastric carcinoma, bronchial carcinoma
- Anti-Ri antibody cases cluster particularly around breast and gynecologic cancers
- Idiopathic cases occur
- Severity ranges from opsoclonus with mild truncal ataxia to severe encephalopathy, coma, and death
Clinical Presentation
Children:
- Subacute onset with staggering and falling (may mimic acute cerebellitis)
- Followed by body jerks, drooling, refusal to walk or sit
- Ataxia, opsoclonus, hypotonia, irritability, sleep disturbance
Adults:
- Mild: opsoclonus with truncal ataxia
- Severe: opsoclonus + myoclonus + ataxia + encephalopathy → stupor → death
- Anti-Ri cases may additionally show muscle rigidity, laryngeal spasms, autonomic dysfunction, and stimulus-sensitive myoclonus
Investigations
| Test | Purpose |
|---|---|
| MRI brain/spine | Usually normal; mild changes possible |
| CSF | Mild pleocytosis in some; oligoclonal bands occasionally |
| Serum/CSF antibodies | Anti-Ri, anti-Hu, GlyR (most are negative) |
| Urine VMA & HVA | Screen for neuroblastoma in children |
| CT/MRI chest & abdomen | Tumor search (all ages) |
Treatment
Treatment has two pillars: immunotherapy and tumor treatment.
Immunotherapy
- Corticosteroids (first-line in children and adults)
- ACTH — effective in most children with neuroblastoma-associated OMAS
- Plasma exchange (PLEX)
- IVIg (intravenous immunoglobulin)
- Rituximab — used in children with refractory/relapsing disease
- Cyclophosphamide — for refractory pediatric cases
Tumor Treatment
- Resection of neuroblastoma in children → resolution of neurological signs in many
- Prompt tumor treatment in adults → better neurological outcome
- Without tumor treatment, the syndrome often progresses to severe encephalopathy and death
Symptomatic
- Sleep disturbance in children may respond to trazodone
Prognosis
| Population | Outcome |
|---|---|
| Children (neuroblastoma) | Ocular and motor symptoms may resolve; most are left with cognitive/behavioral deficits, language and psychomotor delays |
| Adults (tumor treated promptly) | Better neurological outcome |
| Adults (tumor untreated) | Progression to severe encephalopathy and death |
| Overall | Prognosis is somewhat better than other paraneoplastic syndromes; early treatment critical |
Key Points Summary
- OMAS = chaotic saccades (opsoclonus) + myoclonus + cerebellar ataxia
- Children → think neuroblastoma first (>50%); check urine catecholamines
- Adults → think SCLC, breast, ovarian cancer; check anti-Ri, anti-Hu
- Most patients are antibody-negative — serology does not exclude the diagnosis
- Pathophysiology: fastigial nucleus disinhibition
- Treat the tumor + give immunotherapy (steroids, ACTH, PLEX, IVIg, rituximab)
- Pediatric survivors carry long-term neurodevelopmental morbidity
Sources: Adams and Victor's Principles of Neurology 12e; Harrison's Principles of Internal Medicine 22e (2025); Bradley and Daroff's Neurology in Clinical Practice; Kaplan & Sadock's Comprehensive Textbook of Psychiatry; The Harriet Lane Handbook 23e
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