Renal Disease

Renal disease associated with HIV infection may present as fluid-electrolyte and acid-base abnormalities, acute renal failure, coincidental renal disorders, or a glomerulopathy directly related to underlying HIV infection, the so-called HIV-associated nephropathy (HIVAN). Originally observed in patients with AIDS and referred to as AIDS-associated nephropathy, recent studies have described the characteristic renal changes of HIVAN in both asymptomatic HIV-infected individuals and those with early symptomatic HIV disease, thereby broadening the definition to include all HIV-infected patients. With the advent of the potent protease inhibitor indinavir, renal stones have been reported with increasing frequency. Up to 4% of indinauir recipients experience flank pain, with or without hematuria, while on therapy. Crystallization of drug in the renal collecting system leads to development of "sludge," or frank stones, resulting in renal colic.

Fluid, Electrolyte, and Acid-Base Disorders

Fluid-electrolyte disorders are common in patients with advanced HIV infection. Hyponatremia is noted in up to 40% of hospitalized AIDS patients and occurs in the setting of both hypovolemia and euvolemia. Hypovolemia, most often due to gastrointestinal fluid losses, is the most common cause of hyponatremia among this group of patients.

The syndrome of inappropriate antidiuretic hormone release (SIADH) is responsible for the majority of cases of euvolemic hyponatremia and is most often due to underlying Pneumocystis carinii infection, malignancy, or central nervous system (CNS) disease. The presence of hyponatremia is associated with increased morbidity and mortality, especially in conjunction with certain opportunistic infections, such as cryptococcosis.

Adrenal insufficiency is a less frequent cause of hyponatremia. Although abnormalities of the adrenal glands are frequently reported at autopsy, overt adrenal insufficiency occurs in < 5% of patients. The typical findings of hyponatremia, hyperkalemia, non-anion gap metabolic acidosis, hypovolemia, renal salt wasting, and mild renal insufficiency are usually present in some combination.

Drugs are an important cause of fluid and electrolyte disorders in HIV-infected patients and can mimic the abnormalities associated with adrenal dysfunction. Hyperkalemia and non-anion gap metabolic acidosis have been noted in patients receiving parenteral pentamidine. Amphotericin B is associated with hypokalemia, hypomagnesia, renal tubular acidosis, and renal insufficiency. Foscarnet therapy is associated with decreased levels of ionized calcium and, on occasion, renal insufficiency. Nucleotide analogs, such as cidofovir and adefovir, are associated with renal insufficiency and electrolyte disorders. A Fanconi-like proximal renal tubule disorder, characterized by hypophosphatemia and creatinine elevation, has been observed frequently in patients receiving adefovir; the incidence of this disorder increases dramatically after 24 weeks of adefovir therapy. Chemotherapeutic agents used to treat AIDS-associated malignancies may lead to fluid and electrolyte disturbances through direct nephrotoxicity or gastrointestinal losses associated with prolonged vomiting or diarrhea.