Drug-induced myopathy

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.

Polymyositis is an idiopathic inflammatory myopathy causing symmetric, subacute proximal muscle weakness with no rash, driven by endomysial CD8-positive T-cell invasion of non-necrotic, MHC class I-expressing muscle fibers. It is a diagnosis of exclusion confirmed by muscle biopsy, and first-line treatment is high-dose prednisone with a steroid-sparing agent such as methotrexate or azathioprine started concurrently.

Dermatomyositis is a complement-mediated inflammatory myopathy causing symmetric proximal weakness with pathognomonic skin findings, heliotrope rash and Gottron papules, that separate it from polymyositis. It carries a 3- to 12-fold increased malignancy risk and a distinct interstitial lung disease burden that drive workup and therapy. First-line treatment is high-dose prednisone with an early steroid-sparing agent.

Inclusion body myositis is a sporadic inflammatory myopathy of older adults that breaks the pattern of the other myositides: it favors men, causes insidious, often asymmetric weakness of the finger flexors and quadriceps plus dysphagia, and raises creatine kinase only mildly. Biopsy shows endomysial inflammation with rimmed vacuoles and congophilic amyloid inclusions. It does not respond to glucocorticoids or immunosuppression, so treatment centers on structured exercise and physical therapy, dysphagia evaluation and swallowing therapy, and falls prevention.

Myasthenia gravis is an autoimmune disorder of the postsynaptic neuromuscular junction, most often caused by acetylcholine receptor antibodies, producing fluctuating, fatigable weakness of ocular, bulbar, and limb muscles. Diagnosis rests on antibody testing and electrodiagnostics; first-line treatment is pyridostigmine, with glucocorticoids and steroid-sparing immunosuppression for generalized disease and thymectomy for eligible patients.

Hypothyroidism is thyroid hormone deficiency, most commonly caused by autoimmune (Hashimoto) thyroid failure in iodine-sufficient countries, diagnosed by an elevated thyroid-stimulating hormone with a low or normal free thyroxine. First-line treatment is levothyroxine dosed at 1.6 mcg/kg lean body weight orally once daily, titrated using thyroid-stimulating hormone rechecked no sooner than 6 weeks after any dose change.

Polymyalgia rheumatica (PMR) is an inflammatory disorder of older adults causing aching and prolonged morning stiffness of the shoulder and hip girdles with elevated inflammatory markers, but without true weakness and with a normal creatine kinase. It is a clinical diagnosis, and treatment begins with prednisone 12.5 to 25 mg/day, which produces a dramatic response within days.

Acute kidney injury is a sudden rise in serum creatinine or fall in urine output from prerenal, intrinsic, or postrenal causes, defined and staged by KDIGO criteria. Management targets the underlying cause, corrects volume and electrolyte derangements, and escalates to renal replacement therapy for refractory hyperkalemia, acidosis, volume overload, or uremia.

Chronic kidney disease is abnormal kidney structure or function present for more than 3 months, staged by the Kidney Disease: Improving Global Outcomes (KDIGO) system using estimated glomerular filtration rate and albuminuria, and managed with blood pressure control, renin-angiotensin blockade, an SGLT2 inhibitor, and correction of its metabolic complications.

Systemic lupus erythematosus is a chronic multisystem autoimmune disease in which antinuclear and other autoantibodies drive immune-complex deposition and organ injury across skin, joints, kidneys, blood, serosa, and the nervous system. Diagnosis rests on a positive antinuclear antibody plus weighted 2019 EULAR/ACR criteria totaling 10 or more points. Hydroxychloroquine is lifelong first-line therapy for nearly every patient, with glucocorticoids and steroid-sparing immunosuppression added for moderate to severe or organ-threatening disease.

Gout is a crystal arthropathy in which monosodium urate deposits from chronic hyperuricemia trigger acute inflammatory arthritis, classically podagra of the first metatarsophalangeal joint. Diagnosis rests on negatively birefringent needle-shaped crystals in synovial fluid, and treatment pairs anti-inflammatory therapy for the flare with lifelong urate-lowering therapy to a serum urate below 6 mg/dL.

Alcohol use disorder is a chronic pattern of drinking meeting 2 or more of 11 DSM-5 criteria within a 1-year period, screened with the CAGE or AUDIT-C and confirmed by history. First-line management combines a brief behavioral intervention and cognitive behavioral therapy with naltrexone or acamprosate, reserving disulfiram for highly motivated patients who can maintain abstinence.

Cocaine use disorder is a pattern of cocaine use causing significant impairment or distress, distinct from acute intoxication, diagnosed when a patient meets at least 2 of 11 DSM-5 substance use criteria within 12 months. Acute cocaine-associated chest pain is managed first with a benzodiazepine, then nitrates or a calcium channel blocker, while beta blockade is avoided because of concern for unopposed alpha stimulation; no medication is approved for the use disorder itself, so treatment rests on psychosocial care.

Toxic and drug-induced peripheral neuropathy is an umbrella of exposure-related nerve injuries from chemotherapy, antimicrobials, cardiac drugs, antiretrovirals, heavy metals, and alcohol; a careful exposure history, EMG/NCS pattern, and removal of the causative agent drive recognition and treatment.

Antiretroviral therapy (ART) combines three or more drugs from at least two classes to suppress HIV replication. First-line therapy is bictegravir/emtricitabine/tenofovir alafenamide or dolutegravir-based triple therapy, started as soon as the patient is ready regardless of CD4 count, and continued for life to prevent AIDS and transmission.