Tubulointerstitial macrophage infiltration in a patient with hypokalemic nephropathy and primary Sjögren's syndrome

Coexistence of Sjögren's Syndrome-associated Interstitial Nephritis and Hypokalemic Nephropathy in a Patient with Distal Renal Tubular Acidosis: A Case Report

A 42-year-old woman presented with muscle weakness and hypokalemic distal renal tubular acidosis (dRTA). Investigations revealed concurrent Sjögren's syndrome (SS) and Hashimoto's thyroiditis contributing to hypokalemic dRTA. A renal biopsy revealed focal tubulointerstitial nephritis (TIN) suggestive of SS-related renal involvement, along with distinctive ischemic glomerular changes and tubular alterations consistent with hypokalemic nephropathy. Rapid improvement in tubular injury markers and hypobicarbonemia followed potassium supplementation, suggesting that hypokalemia contributed to proximal tubular injury. This case underscores the diagnostic challenge posed by the simultaneous presence of TIN and hypokalemic nephropathy, potentially masking hypokalemic nephropathy in patients with hypokalemic dRTA secondary to SS-TIN.

Optical Clearing in the Kidney Reveals Potassium-Mediated Tubule Remodeling

Distal nephron remodeling contributes to the pathophysiology of many clinically relevant scenarios, including diuretic resistance and certain Mendelian disorders of blood pressure. However, constitutive genetic disruptions are likely to have substantial developmental effects in this segment, and whether tubule remodeling upon physiological stimuli is a normal homeostatic mechanism is not known. Since the distal nephron acts as a potassium sensor, we assessed proliferation and tubule length in three dimensions upon dietary or inducible genetic manipulation by using optical clearing of adult mouse kidneys, whole-mount immunolabeling, and advanced light microscopy. We show that dietary potassium restriction leads promptly to proliferation of various nephron segments, including the distal convoluted tubule, whereas disruption of the potassium sensor Kir4.1 causes atrophy, despite ambient hypokalemia. These results provide proof that kidney tubules adapt rapidly to diet and indicate the power of clearing approaches to assess cell number and tubule length in healthy and diseased kidney.

Renal involvement in primary Sjögren's syndrome: a clinicopathologic study

BACKGROUND & OBJECTIVES

Renal pathology and clinical outcomes in patients with primary Sjögren's syndrome (pSS) who underwent kidney biopsy (KB) because of renal impairment are reported.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twenty-four of 7276 patients with pSS underwent KB over 40 years. Patient cases were reviewed by a renal pathologist, nephrologist, and rheumatologist. Presentation, laboratory findings, renal pathology, initial treatment, and therapeutic response were noted.

RESULTS

Seventeen patients (17 of 24; 71%) had acute or chronic tubulointerstitial nephritis (TIN) as the primary lesion, with chronic TIN (11 of 17; 65%) the most common presentation. Two had cryoglobulinemic GN. Two had focal segmental glomerulosclerosis. Twenty patients (83%) were initially treated with corticosteroids. In addition, three received rituximab during follow-up. Sixteen were followed after biopsy for more than 12 mo (median 76 mo; range 17 to 192), and 14 of 16 maintained or improved renal function through follow-up. Of the seven patients presenting in stage IV chronic kidney disease, none progressed to stage V with treatment.

CONCLUSIONS

This case series supports chronic TIN as the predominant KB finding in patients with renal involvement from pSS and illustrates diverse glomerular lesions. KB should be considered in the clinical evaluation of kidney dysfunction in pSS. Treatment with glucocorticoids or other immunosuppressive agents appears to slow progression of renal disease. Screening for renal involvement in pSS should include urinalysis, serum creatinine, and KB where indicated. KB with characteristic findings (TIN) should be considered as an additional supportive criterion to the classification criteria for pSS because it may affect management and renal outcome.

Hypokalemic nephropathy is associated with impaired angiogenesis

Hypokalemic nephropathy is associated with alterations in intrarenal vasoactive substances, leading to vasoconstriction, salt-sensitivity, and progression of interstitial fibrosis. In this study, we investigated whether hypokalemic nephropathy might also involve impaired renal angiogenesis. Sprague-Dawley rats that were fed low-potassium diets developed peritubular capillary loss that began in the inner stripe of the outer medulla (week 2) and progressed to the outer stripe of the outer medulla (week 4) and cortex (week 12). These changes were associated with increased macrophage infiltration, increased expression of both monocyte chemoattractant protein-1 and TNF-alpha, and a loss of vascular endothelial growth factor and endothelial nitric oxide synthase. Renal thiobarbituric acid-reactive substances, markers of oxidative stress, were increased late in disease. In conclusion, hypokalemic nephropathy is associated with impaired renal angiogenesis, evidenced by progressive capillary loss, reduced endothelial cell proliferation, and loss of VEGF expression.