What autoimmune and paraneoplastic etiologies should be considered in a 3‑year‑old child presenting with sudden‑onset ataxia, nystagmus, and hypertension?

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Last updated: September 14, 2026 • View editorial policy

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Autoimmune and Paraneoplastic Causes in Pediatric Acute Ataxia with Nystagmus and Hypertension

In a 3-year-old with sudden-onset ataxia, nystagmus, and hypertension, you must immediately consider MOG antibody-associated encephalitis, NMDAR encephalitis, GABAB receptor encephalitis, and opsoclonus-myoclonus-ataxia syndrome (OMAS), while simultaneously screening for neuroblastoma given the age and hypertension.

Priority Diagnostic Workup

Immediate Testing Required

Send serum and CSF for the following antibodies simultaneously 1, 2:

  • MOG antibodies (most likely given age, severity, and cerebellar involvement) 3
  • NMDAR antibodies (common in pediatrics, can present with ataxia and movement disorders)
  • GABAB receptor antibodies (specifically associated with opsoclonus, ataxia, and seizures in a reported 3-year-old) 4
  • Anti-Hu, anti-Yo (PCA-1), anti-Ri antibodies (paraneoplastic markers) 5
  • Anti-Ma2 antibodies (recently described with nystagmus as core feature in pediatric cerebellar ataxia) 6
  • CSF oligoclonal bands and IgG index (positive in 77.7% of seronegative autoimmune cerebellar ataxia) 3

Critical Imaging and Ancillary Studies

  • Brain MRI with contrast: Look for cerebellar hyperintensities, brainstem involvement, and multifocal lesions. MOG-positive patients show widespread lesions in 42.8% of cases 3
  • Abdominal CT/MRI: Screen for neuroblastoma immediately given the hypertension and age—this is the most common tumor in OMAS and can present with catecholamine-induced hypertension
  • Urine catecholamines (VMA/HVA): Essential for neuroblastoma screening
  • Consider indirect immunohistochemistry (TIIF/IHC): If standard antibody panels are negative, as this can detect intracellular Purkinje cell antibodies in seronegative cases 7

Age-Specific Considerations for 3-Year-Olds

The combination of ataxia, nystagmus, and hypertension in a 3-year-old creates a unique differential:

  • Neuroblastoma-associated OMAS is the most common paraneoplastic syndrome at this age and directly explains the hypertension through catecholamine excess
  • MOG antibody disease presents more severely in younger children with higher acute mRS scores (mean 3.07) and multifocal MRI abnormalities 3
  • GABAB receptor encephalitis has been documented in a 3-year-old presenting with opsoclonus, ataxia, and chorea—this patient had an aggressive course requiring ICU care 4

Immediate Treatment Algorithm

Do not wait for antibody results before starting immunotherapy 1, 2:

First-Line Therapy (Start Immediately After Ruling Out Infection)

  1. If no contraindications: IV methylprednisolone 30 mg/kg/day (max 1g) for 3-5 days 1

    • Contraindication note: Uncontrolled hypertension is a relative contraindication to steroids 1, so optimize blood pressure control first if severely elevated

  2. If steroids contraindicated or severe presentation: Start combination therapy immediately 1

    • IVIG 2 g/kg divided over 2-5 days PLUS
    • Consider plasma exchange if severe hyponatremia or high thromboembolic risk

Second-Line Therapy (If No Improvement in 2-4 Weeks)

  • For suspected antibody-mediated disease (MOG, NMDAR, GABAB): Rituximab 375 mg/m² weekly × 4 doses 1
  • For paraneoplastic syndromes with intracellular antibodies (anti-Hu, anti-Yo): Consider cyclophosphamide for cell-mediated immunity 1

Paraneoplastic Screening Strategy

Given the age and presentation, prioritize neuroblastoma screening:

  • Abdominal/chest CT with contrast
  • Urine catecholamines
  • If negative and antibodies suggest paraneoplastic etiology, consider whole-body FDG-PET 1

Critical pitfall: In the reported 7-year-old with anti-Yo (PCA-1) antibodies, the instigating adrenal adenocarcinoma had been resected 5 years prior, yet paraneoplastic cerebellar degeneration still occurred 5. This emphasizes that cancer history matters even if remote.

Prognostic Indicators

Predictors of MOG antibody positivity (which has implications for treatment intensity) 3:

  • Younger age (OR 0.718 per year)
  • Higher acute mRS score (OR 5.917)
  • Cranial MRI abnormalities (OR 27.746)

Response patterns:

  • MOG and NMDAR cases typically respond to first-line immunotherapy within weeks 2
  • Paraneoplastic syndromes with intracellular antibodies (anti-Yo, anti-Hu) respond poorly to immunotherapy alone and require tumor treatment 5
  • Seronegative cases with positive oligoclonal bands show good response to prolonged corticosteroids 7

Special Consideration for Hypertension

The hypertension in this case is a critical clue pointing toward:

  1. Neuroblastoma (catecholamine excess)
  2. Posterior reversible encephalopathy syndrome (PRES) as a complication
  3. Relative contraindication to high-dose steroids until blood pressure is controlled 1

Manage hypertension aggressively before initiating steroids to avoid complications, but do not delay IVIG or plasma exchange if steroids are contraindicated.

References

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