Fluctuating subacute generalized weakness

Specialty: General.

• fluctuating general asthenia
• intermittent body weakness lasting weeks
• variable muscle fatigue

Why it occurs

• Myasthenia gravis with generalized initial presentation (characterized by fluctuating muscle weakness that worsens with repeated use of the muscle and improves with rest)
• Potassium metabolism disorders (thyrotoxic or familial hypokalemic periodic paralysis, where weakness occurs in subacute crises interspersed with normal periods)
• Episodes of chronic adrenal insufficiency with intermittent peaks of decompensation (partial addison's crises triggered by minor stressors)
• Multiple sclerosis in the initial flare-up phase (focal demyelination of the motor pathway that causes transient weakness that lasts weeks and then improves)
• Fluctuating somatization disorders associated with variable levels of stress or severe existential anxiety.

Initial workup

Needle electromyography and conduction velocity with low-frequency repetitive stimulation (to evaluate neuromuscular plate fatigue), antibodies against acetylcholine receptor (anti-AChR) and against muscle-specific tyrosine kinase (anti-MuSK), thyroid profile, morning serum cortisol, and blood electrolytes.

Standard management

• Pyridostigmine — 60 mg orally every 6 hours under strict medical supervision, indicated as first line if myasthenia gravis is confirmed
• Potassium chloride — 20 to 40 mEq daily orally if fluctuations are associated with recurrent moderate hypokalemia
• Prednisone (low initial doses with slow titration under the supervision of a neurology specialist).