Nephrology for General Practice - O.I. Bakaliuk 2003

Renal Pathology in Systemic and Other Diseases
Renal Involvement in Sarcoidosis

Sarcoidosis (Boeck's disease, or Besnier-Boeck-Schaumann disease) is a systemic disorder whose morphological hallmark is non-caseating epithelioid Cell granuloma. The core of these granulomas features an accumulation of macrophages surrounded by lymphocytes, occasional plasma Cells, fibroblasts, and Collagen fibers. The most frequent site of involvement (95–97% of cases) is the mediastinal Lymph Nodes; however, the pathological process may also affect the intrathoracic lymphatic ducts, Liver, Spleen, Skin, visual Organs, and The Nervous system (F.I. Komarov et al., 1991).

It was previously believed that Renal Involvement in sarcoidosis was rare (occurring in 2–10% of cases, Th. McCurley et al., 1990) and predominantly asymptomatic, manifesting clinically only at the stage of renal failure. According to recent data (R. Mallmann et al., 1997), renal pathology in sarcoidosis occurs in 28–40% of cases.

The Pathogenesis of nephropathies in sarcoidosis, much like the disease itself, remains not fully understood. An immune-complex mechanism is considered to play a leading role in their onset and progression.

Two main clinical and morphological variants of renal involvement are distinguished in this pathology: calcium nephropathy, interstitial nephritis, and Glomerulonephritis (V.L. Dobyn et al., 1991; B.M. Kornev et al., 1991).

Calcium nephropathy resulting from calciuria (62% of cases) and hypercalcemia (10–20% of cases) is a consequence of renal overproduction of the metabolically active form of vitamin D₃ — 1,25(OH₂)D₃. This leads to calcification of the collecting duct epithelium, The Development of interstitial fibrosis, tubular atrophy, and glomerular hyalinosis, subsequently resulting in arterial Hypertension and renal failure. Nephrolithiasis, developing As a result of calcium METABOLISM disorders, can long remain the primary clinical manifestation of sarcoidosis (B.M. Kornev et al., 1991) and is also the most frequent cause of renal failure in sarcoidosis (Fig. 84).

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Fig. 84. Sarcoidosis: a — radiographic presentation of pulmonary involvement, b — left-sided nephrocalcinosis.

Urinalysis reveals moderate proteinuria, microhematuria, and oxalate crystals.

In granulomatous interstitial nephritis, sarcoidal granulomas form within the renal cortex and medulla. Their subsequent sclerosis is accompanied by glomerular hyalinosis, tubular atrophy, and interstitial fibrosis. Clinically, granulomatous interstitial nephritis manifests with a mild urinary syndrome, hyposthenuria, and polyuria. In some cases, granulomas are absent, and the Changes in the interstitium and tubules are non-specific inflammatory in nature (non-granulomatous interstitial nephritis).

Tubular disorders include symptoms of Renal Tubular Acidosis, renal glucosuria, and nephrogenic diabetes insipidus. The urinary syndrome in such cases is characterized by significant proteinuria (up to 3 g/day) and microhematuria. Arterial hypertension occurs intermittently, while Nephrotic Syndrome develops rarely.

The parallel nature of immune shifts in sarcoidosis and amyloidosis—primarily concerning the functional activity of the T-cell immune system—suggests the possibility of amyloidosis developing as yet another variant of renal involvement in this condition (G. Nedelec et al., 1996).