Subacute generalized weakness

Specialty: General.

• subacute lack of strength
• general weakness of weeks of evolution
• progressive muscle fatigue

Why it occurs

• Myopathy due to hyporeactivity or cumulative toxicity of medications (such as long-term glucocorticoids that induce type II fiber atrophy, or antiretrovirals)
• Lambert-Eaton syndrome or myasthenia gravis with atypical presentation (dysfunction of the motor plate due to autoantibodies that progresses in weeks)
• Chronic inflammatory demyelinating polyneuropathy (CIDP) in early stages (immune demyelination of peripheral nerves with progressive symmetrical motor weakness)
• Poorly compensated chronic electrolyte imbalance (hypokalemia due to chronic use of loop diuretics or laxatives, hyponatremia due to SIADH of tumor or occult origin)
• Lysosomal storage diseases or adult-onset glycogenosis with a subacute course.

Initial workup

Needle electromyography and motor and sensory conduction velocities, serum electrolyte dosage (potassium, sodium, calcium, magnesium, phosphorus), serum CPK and aldolase levels, antibodies against voltage-gated calcium channels (for Lambert-Eaton), and antibodies against acetylcholine receptor (anti-AChR).

Standard management

• Adjustment or suspension of myotoxic drugs under close medical supervision
• Potassium chloride — according to deficit, oral dose under strict biochemical control
• Calcium carbonate (500 mg every 12 hours orally if moderate hypocalcemia contributing to muscle weakness is detected).