Younger age, self-reactive antibodies tied to Sjögren’s kidney involvement
Most patients were asymptomatic, but about a third had impaired function
People with primary Sjögren’s disease diagnosed at a younger age and who harbor certain self-reactive antibodies are more likely to have kidney involvement, a study in South Korea suggests.
While most with kidney involvement were asymptomatic, about a third had impaired kidney function when they were diagnosed and 25% saw their kidney function decline over time. Kidney involvement was also associated with a higher risk of lymphoproliferative disease (LPD), where there is an uncontrolled production of lymphocytes, a type of immune cell.
“Renal involvement is a rare manifestation of [primary Sjögren’s]; however, it is associated with impaired renal function and LPD. Therefore, screening for renal involvement is important for preserving renal function and early detection of LPD,” the researchers wrote. The study, “The prevalence, clinical features, and long-term outcome of patients with primary Sjögren’s syndrome with renal involvement,” was published in Scientific Reports.
Sjögren’s disease occurs when the immune system mistakenly launches an inflammatory attack against the glands that produce tears and saliva, resulting in symptoms that often include eye and mouth dryness. Other organs, such as the kidneys, may also be affected. Primary Sjögren’s refers to when the disease appears on its own, without being associated with other autoimmune conditions.
According to researchers, “a limited number of studies report a heterogeneous [variable] long-term prognosis for [primary Sjögren’s disease] with renal involvement.”
Kidney involvement in Sjögren’s
Here, researchers retrospectively studied 1,306 patients with primary Sjögren’s in South Korea. Nearly all were women (98%) with a mean age of 51 at the time of their Sjögren’s diagnosis. Overall, 2.8% had kidney involvement, about half of whom were diagnosed with kidney involvement at the time of their Sjögren’s diagnosis, while 30% started showing signs after being diagnosed. Six patients had kidney disease before their diagnosis.
Kidney involvement was defined as having at least one of the following: metabolic acidosis, which is excess acid in the body, and alkaline urine (a pH of 6.5 or higher); proteins and/or blood in the urine; impaired kidney function (estimated filtration glomerular rate, or eGFR, below 60 mL/min/1.73 m2); and signs of tissue damage in a kidney biopsy.
Patients with kidney involvement were diagnosed with Sjögren’s at a younger age (45.6 vs. 51.5 years) and had a higher prevalence of anti-Ro (100% vs. 82.2%) and anti-La (65.7% vs. 42.3%) antibodies, than those without kidney involvement. Those with kidney involvement also more frequently developed LPD (5.6% vs. 0.4%).
For 452 patients with available data, disease activity was higher in those with kidney disease (a score of 8 vs. 3 in the EULAR Sjogren’s Syndrome Disease Activity Index). Further statistical analysis also indicated that the presence of anti-La antibodies increased the risk of kidney involvement by more than twofold.
To analyze changes in kidney function over time, the researchers carried out a case-control study that compared patients with Sjögren’s and kidney involvement with those who had persistent alkaline urine but no signs of kidney disease, and with those without kidney disease.
Among those with kidney involvement, 33% showed impaired kidney function (eGFR below 60 mL/min/1.73 m2) at the time kidney involvement was diagnosed, and 44% at the last follow-up. Also, one fourth of these patients had a decrease of more than 20% in eGFR during follow-up. In contrast, 4% of the patients without kidney involvement and 5% with alkaline urine had impaired kidney function, although eGFR didn’t change significantly or drop below 60 mL/min/1.73 m2.
Impaired kidney function at the last visit was inversely associated with levels of hemoglobin — the protein that carries oxygen in red blood cells — and eGFR at the time of Sjögren’s or kidney disease diagnosis. Also, those with Sjögren’s disease and kidney involvement were almost five times more likely to develop LPD.
“Because onset of renal involvement in [primary Sjögren’s] is insidious and asymptomatic, regular monitoring of [blood] and urine electrolytes together with urine pH, sediment, and protein levels is important for early detection,” the researchers wrote, noting that “renal involvement is a predisposing factor for [LPD] in patients with [primary Sjögren’s].”
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