Inflammation within the kidney predominantly affecting tubules. Often seen in conjunction with glomerulonephritis, but then usually regarded as secondary to the glomerular disease. Acute interstitial nephritis is uncommon but important, as prompt therapy can save renal function.
Often difficult as there may be minimal or no symptoms, and minor urine dipstick abnormalities. Urine often contains white blood cells. Blood tests show renal impairment.
- Allergic – the commonest cause is an allergic reaction to a drug, particularly non-steroidal anti-inflammatory drugs (NSAID) or antibiotics, or proton pump inhibitors (PPIs). Variable time after commencement. Usually responds to withdrawal of the drug and treatment with corticosteroids, which may need to be continued for some weeks.
- Immune – as a part of a multisystem autoimmune disease or alone. It is a major feature of renal transplant rejection.
- Toxic – a number of toxins can do this. The commonest is immunoglobulin light chains, produced in excess in myeloma. These are filtered freely at the glomerulus but may prove toxic to tubular cells which reabsorb them. Others include heavy metals and plant and fungal toxins.
- Infective – acute interstitial nephritis may be seen in a number of viral and other infections. The presence of large numbers of neutrophils in and around tubules suggests active bacterial infection – pyelonephritis.