Periodic paralysis

Hypokalemia is a serum potassium level below 3.5 mEq/L, most often caused by gastrointestinal or renal potassium losses, and it produces weakness, ileus, and arrhythmia risk through altered membrane excitability. Diagnosis rests on the urine potassium-creatinine ratio to separate renal from extrarenal causes, and treatment is intravenous or oral potassium chloride, with concurrent magnesium repletion, dosed to severity and symptoms.

Hyperkalemia is a serum potassium level above 5.0 mEq/L, most often from decreased kidney excretion, transcellular shifts, or excess intake, with levels above 6.0-6.5 mEq/L or any ECG change constituting a medical emergency from the risk of fatal arrhythmia. Treatment sequences cardiac membrane stabilization with calcium, transcellular potassium shifting with insulin/dextrose and albuterol, then definitive potassium removal with binders, diuretics, or dialysis.

Hyperthyroidism is the clinical syndrome of thyroid hormone excess, produced by a range of causes from Graves disease and autonomously functioning nodules to destructive thyroiditis and exogenous hormone ingestion. Diagnosis begins with a suppressed thyroid-stimulating hormone and elevated free thyroxine, followed by radioactive iodine uptake testing or antibody measurement to identify the cause, and first-line treatment is a beta blocker for symptom control while the underlying cause directs thionamide, radioactive iodine ablation, or thyroidectomy therapy.

Graves disease is an autoimmune disorder in which thyrotropin receptor antibodies stimulate the thyroid, causing hyperthyroidism, and is the most common cause of thyrotoxicosis in iodine-sufficient regions. Diagnosis rests on a suppressed thyroid-stimulating hormone with elevated free thyroxine and positive thyrotropin receptor antibodies, and first-line treatment is a thionamide, most often methimazole, with radioactive iodine or thyroidectomy reserved for recurrence or patient preference.

Guillain-Barre syndrome is an acute, post-infectious autoimmune polyradiculoneuropathy causing rapidly progressive ascending flaccid weakness and areflexia. Diagnosis is clinical, supported by albuminocytologic dissociation on CSF and demyelinating changes on electrodiagnostic studies; first-line treatment is IVIG or plasma exchange with close monitoring for respiratory failure.

Myasthenic crisis is acute, life-threatening respiratory and bulbar failure from severe worsening of myasthenia gravis, distinct from the chronic, ambulatory disease. Diagnosis rests on bedside respiratory monitoring (vital capacity, maximal inspiratory pressure) and distinguishing it from cholinergic crisis (anticholinesterase overtreatment); management is airway protection plus IVIG or plasma exchange.

Botulism is a descending, symmetric flaccid paralysis caused by Clostridium botulinum neurotoxin, which blocks presynaptic acetylcholine release at the neuromuscular junction and autonomic synapses. Diagnosis is clinical, supported by toxin assay of serum, stool, or wound, and management is early antitoxin administration plus supportive respiratory care, since antitoxin halts progression but does not reverse existing paralysis.

Renal tubular acidosis is a normal anion gap metabolic acidosis caused by impaired renal bicarbonate reabsorption (type 2, proximal) or impaired distal acid excretion (type 1, hypokalemic distal, or type 4, hyperkalemic distal from aldosterone deficiency or resistance). The urine anion gap, serum potassium, and urine pH distinguish the three types, which are treated respectively with alkali replacement plus a thiazide, potassium citrate, and correction of the underlying cause plus mineralocorticoid replacement when appropriate.

Primary hyperaldosteronism is autonomous adrenal aldosterone secretion that suppresses renin, producing hypertension with or without hypokalemia and metabolic alkalosis. It is screened with a plasma aldosterone-to-renin ratio and confirmed with a saline infusion or oral sodium loading test. Unilateral adenomas are treated with laparoscopic adrenalectomy, while bilateral hyperplasia is treated with a mineralocorticoid receptor antagonist such as spironolactone.

Rhabdomyolysis is necrosis of skeletal muscle with release of myoglobin, creatine kinase, and intracellular electrolytes into the circulation, diagnosed by a serum creatine kinase at least five times the upper limit of normal (typically over 1500 U/L) with a urine dipstick positive for blood but no red cells on microscopy; treatment is aggressive isotonic intravenous fluid to a urine output of 200 to 300 mL/h and correction of hyperkalemia, with acute kidney injury from pigment nephropathy the dominant complication.

Drug-induced myopathy spans a spectrum from asymptomatic creatine kinase elevation to rhabdomyolysis and is caused by statins (most common), glucocorticoids, colchicine, hydroxychloroquine, zidovudine, amiodarone, alcohol, and cocaine, each with a distinct mechanism, time course, and presentation. The critical distinction is toxic myopathy that resolves with drug withdrawal versus statin-associated anti-HMGCR necrotizing myopathy, which persists after discontinuation and requires immunosuppression.