Renal Involvement in Idiopathic Inflammatory Myopathies.

Renal involvement in idiopathic inflammatory myopathies is not as uncommon as was previously thought, as it develops in about one fifth of patients. Clinical presentation includes either acute kidney injury or chronic glomerulonephritis. The former usually develops abruptly during acute phases of rhabdomyolysis: in this case, kidney injury is caused by the toxic effects that myoglobinuria has on the kidney tubules, including cast formation and iron-induced oxidative stress and the development of a third space into the injured muscles. The latter instead has an autoimmune nature, a pleomorphic histological picture, and a more indolent course, with the exception of crescentic glomerulonephritis. Accurate diagnosis and management is crucial for these patients, as timely evaluation and treatment can prevent most of the complications. In the setting of rhabdomyolysis-induced acute kidney injury, the necessity of dialysis can be avoided through aggressive hydration and alkalinization, in order to force diuresis and avoid acidosis and hyperkalemia. In immune-mediated glomerulonephritis, renal biopsy is of undoubtedly value in the diagnostic process and can add prognostic and therapeutic information. In these forms, the development of chronic kidney disease can be prevented or at least delayed by the institution or modification of immunosuppressive treatment. Moreover, the use of drugs that inhibit the renin-angiotensin-aldosterone system and some lifestyle modifications, such as smoking cessation, weight loss, and salt restriction have also value in reducing proteinuria and the progression of kidney damage. In this review, we have summarized the currently available evidence and the different case series in an attempt to provide the readers with the most complete and practical notions that are needed to handle these delicate patients.