Calciphylaxis, a rare and potentially fatal disorder seen predominantly among patients with end-stage renal disease, has been increasing significantly in incidence, according to researchers who developed a novel algorithm to characterize the disorder’s epidemiology.

The study, published online in the Journal of General Internal Medicine (JGIM), also showed that chronic hemodialysis (HD) patients with calciphylaxis have mortality rates 2.5 to 3.0 times higher than their counterparts without calciphylaxis.

“To the best of our knowledge, ours is the first study to systematically investigate the incidence and mortality of calciphylaxis at a national level in the United States,” the authors wrote.

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The investigators, led by Sagar U. Nigwekar, MD, of Harvard Medical School in Boston, noted that the absence of a unique International Classification of Disease (ICD) code impedes the identification of calciphylaxis in large administrative databases, such as the U.S. Renal Data System (USRDS) database.Dr. Nigwekar’s group observed that calciphylaxis is included, along with other diagnoses, in ICD-9 code 275.49 (Other Disorders of Calcium Metabolism). Because calciphylaxis is the only disorder listed under this code that requires a skin biopsy for diagnosis, Dr. Nigwekar and his collaborators theorized that simultaneous application of code 275.49 and skin biopsy procedure codes would accurately identify calciphylaxis cases.

They developed the algorithm using the Partners Research Patient Data Registry, identifying 11,451 patients on chronic hemodialysis (HD) during a 10-year study period (January 2002 to December 2011). The researchers identified 74 incident cases of calciphylaxis. They then used the algorithm to determine the incidence of calciphylaxis and associated mortality using the USRDS database and the same study period.

The researchers noted that calciphylaxis incidence spiked during 2006–2007, and this corresponded with the addition of calciphylaxis under code 275.49 in October 2006. Still, calciphylaxis incidence continued rising even after limiting their analysis to 2007 onward. The incidence per 10,000 chronic HD patients rose significantly from 3.7 in 2007 to 5.7 in 2011.

“Future patient-oriented research is needed to understand risk factors and pathogenesis of calciphylaxis,” Dr. Nigwekar told Renal & Urology News. “Our study also serves as a template for investigations in other rare diseases and was selected for publication in the Agency for Healthcare Research and Quality-supported supplement to JGIM dedicated to innovative research addressing rare diseases.”