Chronic tubulointerstitial nephritis

Acute interstitial nephritis (AIN) is inflammation and edema of the renal tubulointerstitium, most commonly a delayed hypersensitivity reaction to a drug, that presents as acute kidney injury with pyuria and leukocyte casts and only occasionally the classic fever-rash-eosinophilia triad. Diagnosis rests on drug history plus a compatible urinalysis, with biopsy reserved for diagnostic uncertainty or failure to improve after the culprit drug is stopped; management is withdrawal of the offending agent, with glucocorticoids for those who do not recover.

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.

Lithium carbonate is the reference mood stabilizer for bipolar disorder, first-line for acute mania and long-term maintenance, and the only mood stabilizer credited with reducing suicide risk. Dosing is titrated to a trough serum level, targeting 0.8 to 1.2 mEq/L for acute mania and 0.6 to 1.0 mEq/L for maintenance. Its narrow therapeutic index and near-total renal clearance make dehydration, renal impairment, and interacting drugs the leading triggers of toxicity, which is treated with isotonic fluids and, when severe, hemodialysis.

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.

Renal papillary necrosis is ischemic coagulative necrosis of the renal medullary pyramids and papillae, most often from sickle cell disease or trait, chronic NSAID/analgesic use, diabetes mellitus, or acute pyelonephritis (the SAAD mnemonic), presenting with gross or microscopic hematuria and sometimes flank pain. It is a clinical diagnosis of exclusion, supported by mild pyuria and proteinuria on urinalysis and confirmed on noncontrast CT showing sloughed papillae, and management is discontinuation of the offending agent and treatment of the underlying cause, since no disease-specific drug therapy exists.

IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder in which tumefactive, IgG4-plasma-cell-rich lesions with storiform fibrosis and obliterative phlebitis enlarge and scar multiple organs, mimicking malignancy at every site. Diagnosis requires biopsy, since a raised serum IgG4 is neither necessary nor sufficient, and first-line treatment is high-dose glucocorticoids with rituximab for relapsing or refractory disease.

Sjogren syndrome is a systemic autoimmune exocrinopathy in which lymphocytic infiltration of the lacrimal and salivary glands causes keratoconjunctivitis sicca and xerostomia, occurring alone (primary) or alongside another rheumatologic disease such as rheumatoid arthritis or lupus (secondary). Diagnosis combines the anti-Ro (SSA) and anti-La (SSB) antibody panel, objective dryness testing, and labial salivary gland biopsy under the 2016 ACR/EULAR classification criteria. Management centers on sicca-directed therapy, pilocarpine or cevimeline for xerostomia and topical cyclosporine for keratoconjunctivitis, with hydroxychloroquine or immunosuppression for extraglandular disease.

Sarcoidosis is a multisystem granulomatous disease of unknown cause defined by noncaseating granulomas, most commonly involving the lungs and hilar lymph nodes. Most patients are asymptomatic or have a self-limited course staged by chest radiograph; symptomatic organ-threatening disease is treated with systemic glucocorticoids, with methotrexate or another steroid-sparing agent added for glucocorticoid-refractory or glucocorticoid-intolerant disease.

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.

Cast nephropathy (myeloma kidney) is acute or subacute kidney injury caused by intratubular obstruction from free light chain and Tamm-Horsfall protein casts, occurring almost exclusively in multiple myeloma with markedly elevated serum free light chains. Treatment is emergency chemotherapy to rapidly lower free light chain production, combined with aggressive isotonic hydration and avoidance of nephrotoxins.

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.

Nephrogenic diabetes insipidus is partial or complete resistance of the renal collecting duct to antidiuretic hormone, most often from chronic lithium therapy, hypercalcemia, or hypokalemia in adults, producing dilute polyuria and compensatory polydipsia. Diagnosis rests on hypernatremia with inappropriately dilute urine that fails to concentrate after desmopressin, and management is stopping the offending drug or correcting the electrolyte abnormality when possible plus a low-sodium, low-protein diet with a thiazide diuretic, adding amiloride if polyuria persists or lithium must continue.

Urinary tract obstruction (obstructive uropathy) is mechanical blockage of urine flow anywhere from the renal pelvis to the urethral meatus, producing hydronephrosis and, when bilateral or affecting a solitary kidney, postrenal acute kidney injury. Diagnosis is by renal/bladder ultrasound showing hydronephrosis or an elevated post-void residual, and management is prompt decompression, urethral or suprapubic catheterization for bladder outlet obstruction or percutaneous nephrostomy/ureteral stenting for upper-tract obstruction, followed by definitive treatment of the underlying cause, with generally good renal recovery if relieved within 1 to 2 weeks.

Bladder cancer, most often urothelial (transitional cell) carcinoma, is the most common genitourinary malignancy and classically presents as painless gross hematuria in a smoker. Diagnosis requires cystoscopy with biopsy, and management is staged by depth of invasion, from intravesical therapy for non-muscle-invasive disease to radical cystectomy or systemic chemotherapy for muscle-invasive or metastatic disease.