The kidney in rheumatic diseases.

Certain rheumatic diseases are associated with unequivocal renal involvement. Examples are the immune complex mediated glomerular nephritis of systemic lupus erythematosus, the renal involvement in other connected tissue disorders such as polyarteritis nodosa, and the renal amyloid that can complicate rheumatoid arthritis or ankylosing spondylitis. Patients with these complications of rheumatic diseases often develop moderate to severe renal impairment making full investigation including renal biopsy ethical as part of the disease management. As a result there are a substantial number of publications on the pathological findings and progression of such complications. More recently, attention has been directed towards the milder subclinical renal involvement that is increasingly recognised as a feature of rheumatic diseases. Discussion centres on whether this results from the disease, particularly if it has systemic manifestations, or whether it arises from the drug treatment of the disease. Improved methods of monitoring renal function would be welcome but the degree of involvement rarely justifies a renal biopsy. The clinician needs simple tests that can alert him to those patients who may require closer surveillance or be at risk. These practical requirements resemble research needs where examination of the urine, a specimen of which can easily be provided by the patient, might be of value in monitoring the progress of rheumatic disease or the extent of tissue breakdown. For this method to be reliable appropriate correction may be necessary for the effect of the disease or the drug treatment, or both, on the kidney. An initial study from Leeds showed an unexpectedly high incidence of renal tubular disorders in unselected patients with rheumatic diseases.' A more extensive follow up failed to find correlations between the renal tubular defect and the use of nonsteroidal anti-inflammatory drugs (NSAIDs) or