EpistemisExertion-induced muscle fatigue
Specialty: Musculoskeletal.
Why it occurs
- Myasthenia gravis (autoimmune, due to antibodies against acetylcholine receptors at the neuromuscular junction)
- Mitochondrial or metabolic myopathies (carnitine palmitoyltransferase deficiency, McArdle disease)
- Chronic fatigue syndrome or fibromyalgia
- Muscular channelopathies or congenital myotonias
- Chronic adrenal insufficiency or severe hypothyroidism
- Lambert-Eaton myasthenic syndrome (frequently associated with small cell lung cancer)
Initial workup
Electromyography (EMG) with low and high frequency repetitive stimulation, and single fiber electromyography | Determination of anti-acetylcholine receptor (Anti-AChR) and anti-MuSK antibodies | Determination of lactic acid and pyruvate at rest and after isometric exercise | Muscle biopsy with histochemistry and electron microscopy.
red flags
Rapidly progressive muscle fatigue that in a few hours associates eyelid ptosis, double vision (diplopia), difficulty swallowing solid or liquid foods, dysphonia and progressive inspiratory dyspnea (myasthenic crisis, requiring immediate admission to the ICU for respiratory monitoring and plasmapheresis/immunoglobulins).
Standard management
- Pyridostigmine bromide — 60 mg orally every 4 to 6 hours; acetylcholinesterase inhibitor, based on Myasthenia Gravis
- Prednisone — 0.5-1 mg/kg/day orally as initial immunosuppressant
- Coenzyme Q10 — 100-200 mg/day orally, empirical adjuvant in mitochondrial myopathies
- Azathioprine (100 mg once a day orally as a long-term corticosteroid saver).
Educational guidance for study. It is NOT a prescription recommendation. The actual choice depends on the cause, the patient, and current guidelines.
- Area
- Musculoskeletal
- Listed causes
- 6
- Treatment options
- 4