Management of Arnold Chiari Malformation with Myasthenia Gravis
The management of a patient with both Arnold Chiari malformation and myasthenia gravis requires careful neurological evaluation, respiratory monitoring, and coordinated treatment of both conditions, with priority given to stabilizing myasthenia gravis due to its potential for respiratory compromise.
Diagnostic Workup
For Myasthenia Gravis:
- Acetylcholine receptor (AChR) antibodies and antistriated muscle antibodies
- If AChR antibodies are negative, test for muscle-specific kinase (MuSK) and lipoprotein-related 4 (LPR4) antibodies
- Pulmonary function assessment with negative inspiratory force (NIF) and vital capacity (VC)
- CPK, aldolase, ESR, and CRP to evaluate for concurrent myositis
- Electrodiagnostic studies including repetitive stimulation and jitter studies
- Troponin, ECG, and TTE to rule out concomitant myocarditis 1
For Arnold Chiari Malformation:
- MRI of brain and spine to assess the extent of cerebellar tonsillar herniation, presence of syringomyelia, and any brainstem compression 2
- Neurological examination focusing on cerebellar function, cranial nerves, and signs of increased intracranial pressure
Treatment Algorithm
Step 1: Stabilize Myasthenia Gravis
Grade 2 MG (mild generalized weakness):
- Pyridostigmine starting at 30 mg PO three times daily, gradually increasing to maximum of 120 mg four times daily as tolerated
- Corticosteroids (prednisone 0.5-1.5 mg/kg PO daily) 1
- Strongly consider inpatient care as patients can deteriorate quickly
Grade 3-4 MG (moderate to severe weakness or myasthenic crisis):
- Admit to hospital with ICU capability
- Continue corticosteroids
- Initiate IVIG 2 g/kg IV over 5 days (0.4 g/kg/day) or plasmapheresis for 5 days
- Consider rituximab if refractory to IVIG or plasmapheresis
- Frequent pulmonary function assessment
- Daily neurological evaluation 1
Step 2: Address Arnold Chiari Malformation
- After stabilizing MG symptoms, evaluate need for surgical intervention for Chiari malformation
- Surgical decompression of the foramen magnum may be indicated if there are progressive neurological deficits related to the Chiari malformation 2, 3
- The decision for surgery should consider the stability of MG and potential respiratory complications
Special Considerations
Medication Precautions:
- Avoid medications that can worsen myasthenia gravis:
- β-blockers
- IV magnesium
- Fluoroquinolones
- Aminoglycosides
- Macrolides 1
Respiratory Management:
- Frequent pulmonary function testing
- Low threshold for intubation if respiratory compromise occurs
- Vigilant monitoring for aspiration risk due to potential bulbar weakness
Perioperative Management (if Chiari surgery needed):
- Optimize MG control before any surgical intervention
- Consider plasmapheresis or IVIG before surgery to minimize risk of myasthenic crisis
- Avoid neuromuscular blocking agents during anesthesia when possible
- Postoperative ICU monitoring for respiratory complications
Follow-up Care
- Regular neurological assessments every 3-6 months
- Periodic MRI to monitor Chiari malformation
- Pulmonary function tests to monitor MG status
- Quality of life assessments 4
Pitfalls and Caveats
Diagnostic confusion: Symptoms of Chiari malformation (headache, neck pain, dizziness) may overlap with MG symptoms, complicating diagnosis and treatment assessment.
Respiratory risk: Both conditions can affect respiratory function, with MG causing respiratory muscle weakness and Chiari potentially affecting brainstem respiratory centers. Close respiratory monitoring is essential.
Surgical timing: Surgery for Chiari malformation should be delayed until MG is well-controlled to minimize perioperative risks.
Medication interactions: Corticosteroids used for MG may temporarily worsen symptoms before improvement occurs.
Symptom attribution: Determining which condition is causing specific symptoms can be challenging but is crucial for appropriate treatment.