Nelson Textbook of Pediatrics 22nd Edition — Endocrine myopathies (thyroid, steroid, parathyroid, growth hormone) and toxic myopathies (statins, colchicine, alcohol, zidovudine, critical illness myopathy). CK elevation, proximal weakness, rhabdomyolysis. Treatment focuses on underlying cause and supportive care.
🌐 paeds.online — Pakistan's Pediatric Platform| Disorder | Key Neuromuscular Features | CK | EMG |
|---|---|---|---|
| Hypothyroidism | Proximal weakness, myoedema, delayed reflexes, Hoffman syndrome (pseudohypertrophy), Kocher-Debré-Sémélaigne (infantile) | Elevated | Nonspecific myopathic |
| Hyperthyroidism | Proximal weakness, thyrotoxic periodic paralysis (Asian males), ophthalmopathy, myasthenia gravis association | Normal to mild elevation | Myopathic |
| Cushing syndrome / Steroid myopathy | Painless proximal weakness, truncal obesity, moon facies. 9α-fluorinated steroids (dexamethasone, betamethasone) most likely | Normal | Myopathic (type II fiber atrophy) |
| Hyperparathyroidism | Proximal weakness, fatigability, fasciculations, myotonia (rare) | Normal to mild elevation | Myopathic |
| Acromegaly / GH excess | Proximal weakness, CTS, neuropathy, muscle atrophy/hypertrophy | Normal or elevated | Myopathic |
| Hypoparathyroidism | Tetany (Chvostek, Trousseau), cramps, myopathy | Mild elevation | Multiplex discharges |
| Category | Drugs/Toxins | Mechanism |
|---|---|---|
| Inflammatory | Cimetidine, D-penicillamine, procainamide, L-tryptophan | Immune-mediated |
| Necrotizing / Vacuolar | Statins, chloroquine, colchicine, emetine, amiodarone | Mitochondrial dysfunction / lysosomal |
| Rhabdomyolysis | Statins, alcohol, cocaine, amphetamines, toluene, heroin | Direct toxicity / ischemia |
| Mitochondrial | Zidovudine (AZT), statins, linezolid | Mitochondrial DNA depletion / respiratory chain inhibition |
| Myosin loss | Nondepolarizing neuromuscular blockers + IV glucocorticoids (critical illness myopathy) | Thick filament (myosin) loss |
| Myotonia | Chloroquine, cyclosporine, statins, 2,4-dichlorophenoxyacetic acid | Membrane excitability |
Incidence: Myalgias in 10-20%; myopathy (CK elevation + weakness) less common; immune-mediated necrotizing myopathy (anti-HMGCR antibodies) rare but severe.
Management: Discontinue statin. For immune-mediated myopathy: prednisone, IVIG, rituximab.
Critical illness myopathy: Selective loss of thick (myosin) filaments. Associated with steroids + neuromuscular blocking agents.