Toxic and drug-induced peripheral neuropathy

Diabetic neuropathy is length-dependent nerve damage from chronic hyperglycemia, most often a distal symmetric sensorimotor polyneuropathy causing numbness, pain, and loss of ankle reflexes, with autonomic, mononeuropathy, and radiculoplexus variants. Diagnosis is clinical after excluding other causes; management is tight glycemic control plus gabapentinoid or duloxetine therapy for painful symptoms.

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.

Amiodarone is an iodine-rich class III multichannel antiarrhythmic used for ventricular fibrillation and pulseless ventricular tachycardia in cardiac arrest, sustained ventricular tachycardia, and atrial fibrillation rhythm or rate control when other agents are unsafe. First-line arrest dosing is a 300 mg intravenous push, and long-term use requires monitoring for thyroid, liver, lung, and eye toxicity.

Lead poisoning is chronic accumulation of inorganic lead, most often from lead paint dust in pre-1978 housing in children or occupational inhalation in adults, that inhibits heme synthesis and injures the developing brain and kidneys. Diagnosis rests on a venous blood lead level. Management is graded by that level: mandatory source removal at every threshold, oral succimer for 45 to 69 mcg/dL, and combined dimercaprol plus edetate calcium disodium for encephalopathy or levels of 70 mcg/dL or higher.

Inorganic arsenic poisoning presents acutely with vomiting, profuse diarrhea, garlic-odor breath, and QT prolongation, and chronically with skin pigmentation, hyperkeratosis, and peripheral neuropathy. The mechanism is sulfhydryl-group binding that inhibits lipoic acid and the pyruvate dehydrogenase complex. It is treated with fluid resuscitation and chelation, dimercaprol or succimer, which reverses the systemic illness far better than the neuropathy.

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.

Tuberculosis, caused by Mycobacterium tuberculosis, remains a leading global cause of infectious death and presents as latent infection, primary/secondary pulmonary disease, or extrapulmonary and disseminated (miliary) disease. Diagnosis rests on AFB smear, NAAT, and mycobacterial culture (the gold standard), and drug-susceptible active disease is treated with a four-drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol) for 2 months followed by isoniazid plus rifampin for 4 to 7 months.

Vitamin deficiency and toxicity syndromes cluster into fat-soluble (A, D, E, K) and water-soluble (B1, B3, B6, B9, B12, C) patterns that arise mainly from malabsorption, bariatric surgery, alcohol use, or restricted diets. Recognizing the clinical syndrome and confirming it with the specific vitamin level allows targeted repletion, while excess supplementation drives the mirror-image toxicity syndromes.

Carpal tunnel syndrome is compression of the median nerve at the wrist causing pain, paresthesia, and eventually weakness in the thumb, index, middle, and radial half of the ring finger, treated first with neutral wrist splinting and, when refractory, with corticosteroid injection or surgical decompression.

The most common inherited peripheral neuropathy, comprising more than 70 genetic subtypes that cause slowly progressive distal weakness, sensory loss, areflexia, and foot deformity; diagnosis rests on nerve conduction studies and confirmatory genetic testing, and management is supportive since there is no disease-modifying drug therapy.

Cryoglobulinemia is the presence of immunoglobulins that precipitate below 37 degrees Celsius, classified as type I (monoclonal, driven by a lymphoproliferative disorder, causing hyperviscosity) or mixed types II/III (immune-complex, driven mainly by hepatitis C virus infection, causing small-vessel vasculitis). Type I is treated by targeting the underlying clonal disorder; mixed disease is treated with direct-acting antiviral therapy for hepatitis C, escalating to glucocorticoids plus rituximab for organ-threatening vasculitis.

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.

Celiac disease is an immune-mediated small-intestinal enteropathy triggered by dietary gluten in genetically predisposed individuals, presenting with malabsorptive diarrhea, iron-deficiency anemia, or dermatitis herpetiformis. Diagnosis requires IgA tissue transglutaminase serology with a total IgA level while the patient still eats gluten, confirmed by duodenal biopsy showing villous atrophy, and the only treatment is a strict lifelong gluten-free diet.

Monoclonal gammopathy of unknown significance (MGUS) is an asymptomatic, premalignant plasma cell disorder defined by a serum monoclonal protein under 3 g/dL, clonal marrow plasma cells under 10%, and no myeloma-defining end-organ damage. It is the most common plasma cell dyscrasia, progresses to multiple myeloma or a related malignancy at about 1% per year, and requires no treatment, only periodic surveillance.

Multiple myeloma is a clonal plasma cell neoplasm that produces a monoclonal immunoglobulin and end-organ damage summarized by CRAB (hypercalcemia, renal failure, anemia, bone lesions), diagnosed by marrow clonal plasma cells of 10% or more plus a CRAB or SLiM myeloma-defining event. Treatment combines a proteasome inhibitor, an immunomodulatory drug, and dexamethasone, followed by autologous stem cell transplant and maintenance in eligible patients.

Amyloidosis is extracellular deposition of misfolded protein fibrils that stain apple-green with Congo red under polarized light, most often AL (clonal light chains, linked to plasma cell dyscrasias), AA (chronic inflammation), or ATTR (transthyretin, hereditary or wild-type). Diagnosis requires tissue biopsy for Congo red birefringence plus typing of the amyloid protein, and treatment targets the underlying source, plasma-cell-directed therapy for AL, inflammatory disease control for AA, and transthyretin stabilizers or silencers for ATTR.