Figure 88

Abnormal calcium metabolism and pathophysiology of renal involvement in sarcoidosis. Increased synthesis of calcitriol (1,25-dihydroxy-vitamin D3) by the macrophages of the granulomatous lesions of sarcoidosis are at the core of the abnormal calcium metabolism that accounts for the principal manifestations of renal involvement of sarcoidosis (gray boxes). Patients with hypercalciuria, which by far is the most common, may remain asymp tomatic , and the disease may go undetected. Polyuria and a reduced capacity to concentrate the urine are its main manifestations. Either of these two features may be the result of tubulointerstitial nephritis caused by sar-coidosis, and can be present in the absence of any altered calcium metabolism. Nephrocalcinosis also may be asymptomatic. In contrast, nephrolithiasis presents as renal colic or hematuria. Hypercalcemia develops only when the load of calcium to be excreted exceeds the ability of the kidneys to excrete the calcium load, either because of reduced renal function or, less commonly, when the amount of calcium absorbed is excessive. The magnitude of hypercalcemia determines its symptomatology. The circulating level of parathyroid hormone should be determined in patients with hypercalcemia. An increase in the prevalence of parathyroid adenomas seems to occur in sarcoidosis. In hypercal-cemia caused by elevated levels of calcitriol and by reduced renal excretion of calcium, parathyroid hormone levels should be negligible. Detection of elevated levels of parathyroid hormone should lead to the search for an adenoma. Patient management is directed at reducing calcitriol synthesis by treating the granulomatous lesions with steroids. Equally important measures in the management of such patients are restriction of calcium intake, avoidance of dietary supplements that contain vitamin D, shunning exposure to sunlight, and increased fluid intake.

FIGURE 8-9 (s

Micrograph of granulomatous lesions of the renal interstitium that are observed in 15% to 40% of patients with sarcoidosis. The highest rate reported in the literature is 40%. This figure is based on autopsy findings, which often reveal occasional granulomas of the kidney without any evidence of functional or clinical abnormality. The lower figure of 15%, or less, more clearly reflects diffuse infiltration of the kidneys with granulomas associated with clinical evidence of abnormal renal function, as shown here. Generally, enlarged kidneys are noted on renal ultrasonography.

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