tubulointerstitial

Tubulointerstitial refers to the portion of the kidney that comprises the renal tubules and the surrounding interstitial tissue, including the peritubular capillaries and resident interstitial cells. It lies between the glomeruli and the collecting ducts and is essential for tubular function and interstitial signaling.

The tubulointerstitium contains tubular epithelium, interstitial fibroblasts, immune cells, and the microvasculature. It participates in reabsorption and secretion, helps regulate acid-base and electrolyte balance, and responds to injury with inflammatory and fibrotic processes.

Tubulointerstitial diseases describe pathologies that predominantly affect the tubules and interstitium rather than the glomeruli. They are commonly classified as acute or chronic. Acute tubulointerstitial nephritis features interstitial edema with inflammatory cell infiltration, tubular injury, and sometimes eosinophilia. Chronic tubulointerstitial nephritis shows tubular atrophy and interstitial fibrosis, with progressive loss of nephrons and declining kidney function.

Etiologies include drug-induced injury (such as nonsteroidal anti-inflammatory drugs, certain antibiotics, and diuretics), infections, autoimmune diseases (notably Sjögren syndrome and systemic lupus erythematosus), ischemia, toxins, and urinary tract obstruction. Analgesic nephropathy is a historical example of chronic tubulointerstitial injury.

Diagnosis relies on clinical context, laboratory findings (elevated creatinine, sterile pyuria, and sometimes eosinophils in urine), and, when necessary, renal biopsy showing interstitial inflammation or fibrosis with tubular damage. Imaging is often nonspecific.

Management centers on removing the inciting cause, treating the underlying disease, and providing supportive care. Corticosteroids are used selectively for certain forms of acute tubulointerstitial nephritis and some chronic cases. Prognosis depends on the extent of interstitial fibrosis and tubular atrophy.