Neurology · Year 3 · from Neurology

Case 2: Myasthenia Gravis

Patient Demographics

• Age: 32 years
• Sex: Female
• Occupation: Nurse

Chief Complaint

"My eyelids droop and I see double, especially at the end of the day."

History of Present Illness

The patient first noticed drooping of her right eyelid 3 months ago. It was intermittent, worse in the evening and after reading. Over time, both eyelids became affected, and she developed double vision. She has also noticed that her voice becomes weak and nasal after talking for extended periods, and she has difficulty swallowing pills. Recently, she has noticed weakness in her arms when brushing her hair and difficulty climbing stairs. Symptoms improve after rest or sleep. She was recently diagnosed with hypothyroidism. No respiratory symptoms at this time.

Neurological Examination Findings

Mental Status:

• Alert, oriented, normal cognition

Cranial Nerves:

• CN II: Visual acuity normal
• CN III, IV, VI:
• Bilateral ptosis - right worse than left
• Ptosis worsens with sustained upgaze (fatigable ptosis)
• Curtain sign positive: Manually elevating drooping lid worsens ptosis on other side
• Ophthalmoparesis: Variable weakness, not conforming to single nerve
• Diplopia on lateral gaze
• Cogan's lid twitch: Brief lid overshoot after looking down then up
• CN VII: Bilateral facial weakness, "snarling" smile
• CN IX, X: Nasal voice after sustained counting, mild dysphagia
• CN XII: Tongue normal

Motor Examination:

• Proximal weakness:
• Deltoids: 4/5 initially, 3/5 after repetitive abduction (fatigable)
• Hip flexors: 4/5
• Distal strength: 5/5
• No muscle atrophy
• Normal tone

Sensory Examination:

• Intact throughout

Reflexes:

• 2+ symmetric
• Plantar responses flexor

Coordination:

• Normal

Respiratory Assessment:

• FVC: 3.2 L (88% predicted) - within normal limits
• No dyspnea

Myasthenia vs Other Causes of Ptosis/Diplopia

Neuro Workup

• Ice Pack Test: Ptosis improves after 2 minutes of ice application (positive - suggests MG)
• Serology:
• Acetylcholine receptor (AChR) antibodies: POSITIVE (diagnostic, 85% sensitivity)
• If negative: Test anti-MuSK antibodies, anti-LRP4 antibodies
• Electrodiagnostic Studies:
• Repetitive nerve stimulation (3 Hz): >10% decremental response in facial and proximal muscles
• Single-fiber EMG: Increased jitter (most sensitive test)
• CT Chest:
• Thymoma identified (10-15% of MG patients have thymoma; 50% of thymoma patients develop MG)
• Pulmonary Function: FVC and NIF baseline
• Thyroid Function: TSH elevated, T4 low (hypothyroidism - autoimmune association)

Diagnosis

Myasthenia Gravis - AChR antibody positive, with thymoma

• MGFA Class IIb: Mild generalized (predominantly limb/axial weakness)

Management

Symptomatic Treatment:

1. Pyridostigmine (Mestinon) 60 mg TID - acetylcholinesterase inhibitor

• Start low, titrate to effect
• Side effects: Cholinergic (diarrhea, cramping, salivation)
• Do not use as monotherapy in moderate-severe disease

Immunosuppressive Therapy:

1. Prednisone 20 mg daily, titrate up to 60-80 mg/day, then slow taper

• Most effective immunotherapy
• Can cause initial worsening (start low, monitor closely)

1. Steroid-sparing agents:

• Azathioprine (first-line adjunct)
• Mycophenolate mofetil

1. For refractory disease: Rituximab, eculizumab (especially MuSK-MG)

Thymectomy:

1. STRONGLY indicated - patient has thymoma
2. Even without thymoma, thymectomy improves outcomes in AChR+ MG
3. Perform after optimization of symptoms

Crisis Prevention:

1. Avoid myasthenia-exacerbating medications:

• Aminoglycosides, fluoroquinolones
• Beta-blockers
• Magnesium
• Botulinum toxin
• Certain anticonvulsants

1. Monitor for myasthenic crisis (respiratory failure)
2. Stress-dose steroids for surgery

Myasthenic Crisis Management (if occurs):

1. ICU admission, intubation if FVC <15 mL/kg or NIF < -20
2. IVIG 2 g/kg over 5 days OR Plasmapheresis (5 exchanges)
3. Identify trigger (infection, medication, surgery)
4. Hold pyridostigmine during intubation (can cause secretions)

Clinical Image

Image Description: CT chest demonstrating an anterior mediastinal mass (thymoma) in a patient with myasthenia gravis.

Attribution: Image from Radiopaedia.org, Case courtesy of Dr. David Cuete. Licensed under CC BY-NC-SA 3.0. Source: https://radiopaedia.org/cases/thymoma-7

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