Moderate and Severe Psoriasis Linked to Higher Kidney Risks

Jenni Laidman

October 16, 2013

People with severe psoriasis are at nearly twice the risk of developing chronic kidney disease (CKD) as those without, according to a study involving more than 800,000 people published October 15 in BMJ. The study also shows an elevated risk for CKD among patients with moderate levels of the autoimmune disease.

The results suggest a need for increased vigilance for CKD among clinicians treating psoriasis patients, Andy Robertson, PhD, chief science and medical officer for the National Psoriasis Foundation, told Medscape Medical News. Dr. Robertson was not involved with the current study. "A fifth to a quarter of all people with psoriasis, probably a million and half people, should be regularly screened for kidney disorders."

Joy Wan, MD, resident physician, Department of Dermatology, University of Pennsylvania, Philadelphia, and colleagues used the physician-maintained medical records of The Health Improvement Network (THIN) to compare patients, aged 18 to 90 years, who have psoriasis with patients without psoriasis matched by age, practice, and time of visit.

They included 142,883 patients with psoriasis, 7354 patients with severe psoriasis, and 689,702 patients without psoriasis (up to 5 control patients per cohort member). Disease severity was identified by the method of treatment. A nested analysis of 8731 psoriasis patients aged 25 to 64 years determined psoriasis severity, using confirmed data about the percentage of body surface area affected in each patient. Each patient with psoriasis in the nested study was matched by age and practice to up to 10 unaffected patients, for a control group of 87,310 patients.

The overall adjusted hazard ratio (AHR) for CKD among patients with mild, moderate, or severe psoriasis was 1.05 (95% confidence interval [CI], 1.02 - 1.07). However, when the researchers stratified the psoriasis patients by disease severity, the risk for those with mild psoriasis dropped to baseline (AHR, 0.99; 95% CI, 0.97 - 1.02), whereas, the AHR for CKD among those with severe psoriasis was 1.93 (95% CI, 1.79 - 2.08). The investigators adjusted for age, sex, cardiovascular disease, diabetes mellitus, hyperlipidemia, hypertension, use of nonsteroidal anti-inflammatory drugs, and body mass index.

In the nested analysis, the adjusted odds ratio (AOR) of CKD among patients with mild psoriasis (those with less than 3% of body area affected) was 0.89 (95% CI, 0.72 - 1.10), but those with moderate psoriasis (with between 3% and 10% of the body surface affected) showed a distinct increased risk for CKD, with an AOR of 1.36 (95% CI, 1.06 - 1.74). In severe cases, in which more than 10% of the body surface area was affected, the AOR for CKD was 1.58 (95% CI, 1.07 - 2.34). The results were adjusted for age, sex, cardiovascular disease, diabetes, hypertension, hyperlipidemia, body mass index, use of nonsteroidal anti-inflammatory drugs, and duration of observation.

Age had a significant effect on risk, with the relative risk for CKD highest in younger patients. A 30-year-old with severe psoriasis had a relative risk (RR) of developing CKD of 3.82 (95% CI, 3.15 - 4.64), whereas the RR for a 60-year-old was 2.00 (95% CI, 1.86 - 2.17).

However, the adjusted attributable risk for CKD still rose with age because of the age-dependent rise in baseline CKD risk. Among 30- to 40-year-olds, the adjusted attributable risk was 2.89 per 1000 persons (95% CI, 2.26 - 3.64), whereas the adjusted attributable risk among 60- to 70-year-olds was 27.93 (95% CI, 23.11 - 33.15). That equates to an excess risk of 1 patient for every 346 CKD cases among 30- to 40-year-olds and 1 patient per every 36 CKD cases among 60- to 70-year-olds. Attributable and excess risk were calculated at the median age in each group, using the AHR for CKD in patients with severe psoriasis.

Sensitivity analyses of the data showed that the increased CKD risk was not a result of psoriasis medications with known nephrotoxicity. When patients receiving methotrexate or cyclosporine were eliminated from the analyses, the increased relative risk was unaffected, the authors write.

The study is part of a growing body of literature defining psoriasis comorbidities, Dr. Robertson said. Previous research has linked the autoimmune disorder with cardiovascular disease, some inflammatory bowel diseases, and some metabolic diseases. "The trend is that we need to think about psoriasis as a systemic disease, not as a skin disease."

Thomas Manley, RN, director of scientific activities for the National Kidney Foundation, said the study confirms earlier, smaller studies looking for a relationship between psoriasis and renal failure.

"This is an elegantly done analysis," Manley told Medscape Medical News. "They did a great job of looking at the possible confounders, and there are obviously a lot of them, and pretty much confirmed the direct association between psoriasis and the development of kidney disease." Manley was not involved with the BMJ study.

One coauthor has received grants from the NephCure Foundation–American Society of Nephrology and the National Kidney Foundation/Amgen Kidney Disease Outcomes Quality Initiative research fellowship; one coauthor has received research grants from Amgen, Abbvie, Eli Lilly, and Novartis and honorariums from Abbvie, Jansen, Novartis, Eli Lilly, and Pfizer and chairs the data and safety monitoring boards for Celgene and Merck. Manley and Dr. Robertson have disclosed no relevant financial relationships.

BMJ. 2013;347:f5961. Full text

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