Weight loss, fatigue, and renal failure

HOW COMMON IS RENAL INVOLVEMENT IN SARCOIDOSIS?

2. What is the likelihood of finding clinically apparent renal involvement in a patient with sarcoidosis?

• Greater than 70%
• Greater than 50%
• Up to 50%
• Less than 10%

The prevalence of renal involvement in sarcoidosis is hard to determine due to differences in study design and patient populations included in the available reports, and because renal involvement may be silent for many years. Recent studies have reported impaired renal function in 0.7% to 9.7% of cases: eg, a case-control study of 736 patients reported clinically apparent renal involvement in 0.7% of patients,⁵ and in a series of 818 patients, the incidence was 1%.⁹ In earlier studies, depending on the diagnostic criteria, the incidence ranged from 1.1% to 9.7%.¹⁰

The prevalence of renal involvement may also be underestimated because it can be asymp­tomatic, and the number of granulomas may be so few that they are absent in a small biopsy specimen. A higher prevalence of renal involvement in sarcoidosis is reported from autopsy studies, although many cases remained clinically silent. These studies have reported renal noncaseating granulomas in 7% to 23% of sarcoidosis patients.^11–13

PRESENTATION OF RENAL SARCOIDOSIS

3. What is the most common presentation in isolated renal sarcoidosis?

• Sterile pyuria
• Elevated urine eosinophils
• Renal insufficiency
• Painless hematuria

Renal manifestations of sarcoidosis include hypercalcemia, hypercalciuria, nephrocalcinosis, nephrolithiasis, and impaired renal function.¹⁴ Renal involvement can occur during the course of existing sarcoidosis, at the time of first presentation, or even as the sole presentation of the disease.^1,11,15 In patients with isolated renal sarcoidosis, the most common presentation is renal insufficiency.^15,16

Two main pathways for nephron insult that have been validated are granulomatous infiltration of the renal interstitium and disordered calcium homeostasis.^11,17 Though extremely rare, various types of glomerular disease, renal tubular defects, and renal vascular involvement such as renal artery granulomatous angiitis have been documented.¹⁸

Hypercalcemia in sarcoidosis

Sarcoidosis is known to cause hypercalcemia by increasing calcium absorption secondary to 1,25-dihydroxyvitamin D production from granulomas. Our patient’s case is unusual, as renal failure was the sole extrapulmonary manifestation of sarcoidosis without hypercalcemia.

In sarcoidosis, extrarenal production of 1-alpha-hydroxylase by activated macrophages inappropriately increases levels of 1,25-dihydroxyvitamin D (calcitriol). Subsequently, serum calcium levels are increased. Unlike its renal equivalent, granulomatous 1-alpha-hydroxylase evades the normal negative feedback of hypercalcemia, so that increased calcitriol levels are sustained, leading to hypercalcemia, often accompanied by hypercalciuria.¹⁹

Disruption of calcium homeostasis affects renal function through several mechanisms. Hypercalcemia promotes vasoconstriction of the afferent arteriole, leading to a reduction in the GFR. Intracellular calcium overload can contribute to acute tubular necrosis and intratubular precipitation of calcium, leading to tubular obstruction. Hypercalciuria predisposes to nephrolithiasis and obstructive uropathy. Chronic hypercalcemia and hypercalciuria, if untreated, cause progressive interstitial inflammation and deposition of calcium in the kidney parenchyma and tubules, resulting in nephrocalcinosis. In some cases, nephrocalcinosis leads to chronic kidney injury and renal dysfunction.

HISTOLOGIC FEATURES

4. What is the characteristic histologic feature of renal sarcoidosis?

• Membranous glomerulonephritis
• Mesangioproliferative glomerulonephritis
• Minimal change disease
• Granulomatous interstitial nephritis
• Immunoglobulin (Ig) A nephropathy

Granulomatous interstitial nephritis is the most typical histologic feature of renal sarcoidosis.^4,20–22 However, interstitial nephritis without granulomas is found in up to one-third of patients with sarcoid interstitial nephritis.^15,23

Patients with sarcoid granulomatous interstitial nephritis usually present with elevated serum creatinine with or without mild proteinuria (< 1 g/24 hours).^1,15,16 Advanced renal failure (stage 4 or 5 chronic kidney disease) is relatively common at the time of presentation.^1,15,16 In the 2 largest case series of renal sarcoidosis to date, the mean presenting serum creatinine levels were 3.0 and 4.8 mg/dL.^11,15 The most common clinical syndrome associated with sarcoidosis and granulomatous interstitial nephritis is chronic kidney disease with a decline in renal function, which if untreated can occur over weeks to months.²¹ Acute renal failure as an initial presentation is also well documented.^15,24

Even though glomerular involvement in sarcoidosis is rare, different kinds of glomerulonephritis have been reported, including membranous glomerulonephritis, mesangio­proliferative glomerulonephritis, IgA nephropathy, minimal change disease, focal segmental sclerosis, and crescentic glomerulonephritis.²⁵

DIAGNOSIS OF RENAL SARCOIDOSIS

5. How is renal sarcoidosis diagnosed?

• By exclusion
• Complete urine analysis and renal function assessment
• Renal biopsy
• Computed tomography
• Renal ultrasonography

The diagnosis of renal sarcoidosis is one of exclusion. Sarcoidosis must be considered in the differential diagnosis of renal failure of unknown origin, especially if disordered calcium homeostasis is also present. If clinically suspected, diagnosis usually requires pathohistologic demonstration of typical granulomatous lesions in the kidneys or in one or more organ systems.²⁶

In cases of sarcoidosis with granulomatous interstitial nephritis with isolated renal failure as a presenting feature, other causes of granulomatous interstitial nephritis must be ruled out. A number of drug reactions are associated with interstitial nephritis, most commonly with antibiotics, NSAIDs, and diuretics. Although granulomatous interstitial nephritis may develop as a reaction to some drugs, most cases of drug-induced interstitial nephritis do not involve granulomatous interstitial nephritis.

Other causes of granulomatous interstitial infiltrates include granulomatous infection by mycobacteria, fungi, or Brucella; foreign-body reaction such as cholesterol atheroemboli; heroin; lymphoma; or autoimmune disease such as tubulointerstitial nephritis with uveitis syndrome, granulomatosis with polyangiitis, or Crohn disease.^27,28 The absence of characteristic kidney biopsy findings does not exclude the diagnosis because renal sarcoidosis can be focal and easily missed on biopsy.²⁹

Urinary manifestations of renal sarcoidosis are usually not specific. In renal sarcoidosis with interstitial nephritis with or without granulomas, proteinuria is mild or absent, usually less than 1.0 g/day.^11,15,16 Urine studies may show a “bland” sediment (ie, without red or white blood cells) or may show sterile pyuria or microscopic hematuria. In glomerular disease, more overt proteinuria or the presence of red blood cell casts is more typical.

Hypercalciuria, nephrocalcinosis, and nephrolithiasis are nonspecific abnormalities that may be present in patients with sarcoidosis. In this regard, an elevated urine calcium level may support the diagnosis of renal sarcoidosis.

Computed tomography and renal ultrasonography may aid in diagnosis by detecting nephrocalcinosis or nephrolithiasis.

The serum ACE level is elevated in 55% to 60% of patients with sarcoidosis, but it may also be elevated in other granulomatous diseases or in chronic kidney disease from various causes.⁵ Therefore, considering its nonspecificity, the serum ACE level has a limited role in the diagnosis of sarcoidosis.³⁰ Using the ACE level as a marker for disease activity and response to treatment remains controversial because levels do not correlate with disease activity.^5,11