Infection:
Viral infection (e.g. Influenza)
Bacterial infection
Spirochete infection (E.g. Dengue fever; Trichinella)
Drugs:
Statins
Bisphosphonates
Corticosteroids
Ciprofloxacin
Clofibrate
Colchicine
Chloroquine
Emetine
Aminocaproic acid
Zidovudine
Bretylium
Penicillamine
Drugs causing hypokalemia
Metabolic disorders:
Vitamin D deficiency
Mitochondrial myopathy
Scurvy
Osteomalacia
Fibromyalgia
Endocrine:
Hypothyroidism
Hyperthyroidism
Cushing’s syndrome
Adrenal insufficiency
Hyperparathyroidism
Polymyalgia rheumatica
Rhabdomyolysis
Myositis
Polymyositis
Dermatomyositis
Myositis (peds)
Systemic lupus erythematosus
Rheumatoid arthritis
Inclusion body myositis
Sarcoidosis
Scleroderma
Sjögren’s syndrome
Psychiatric (e.g. somatic manifestations of depression)
Domestic abuse
Crush injury
Lyme disease
Ehlers-Danlos syndrome(hypermobility syndrome)
HIV myopathy
Hypophosphatemia
Hypokalemia
Hypothermia
Prolonged immobility
Strenuous exercise (overuse) or heat stroke
Seizure
Severe volume contraction
Alcoholism
Muscular dystrophy
Duchenne
Becker
Limb-girdle
Facioscapulohumeral
Myotonic dystrophy
Myotonia congenita
Compartment syndrome; Muscle infarction
Neuropathic
Chronic fatigue syndrome
Vasculitis
Sarcocystosis
Spinal stenosis
Diabetic lumbosacral plexopathy
Viral infection (e.g. Influenza)
Bacterial infection
Spirochete infection (E.g. Dengue fever; Trichinella)
Statins
Bisphosphonates
Corticosteroids
Ciprofloxacin
Clofibrate
Colchicine
Chloroquine
Emetine
Aminocaproic acid
Zidovudine
Bretylium
Penicillamine
Drugs causing hypokalemia
Vitamin D deficiency
Mitochondrial myopathy
Scurvy
Osteomalacia
Hypothyroidism
Hyperthyroidism
Cushing’s syndrome
Adrenal insufficiency
Hyperparathyroidism
Polymyositis
Dermatomyositis
Myositis (peds)
Duchenne
Becker
Limb-girdle
Facioscapulohumeral
Myotonic dystrophy
Myotonia congenita
Myalgia
Infection:
Chest pain 
Viral infection 
Dysuria
Bacterial infection
Heat cramps
Spirochete infection 