The association between porphyria cutanea tarda and diabetes mellitus: analysis of a long-term follow-up cohort

Abstract

An association between porphyria cutanea tarda (PCT) and diabetes mellitus (DM) is widely reported, but the pathogenetic link remains unknown. To investigate the natural history of DM in the setting of PCT and to determine which PCT features and risk factors may be associated with the development of DM. This retrospective longitudinal study included 81 Spanish patients with PCT with at least 10 years of strict follow-up. Patients attended our Porphyria Unit for follow-up visits and the data were collected in the period 2004-2008. We classified patients into two groups: patients with glucose metabolism alterations (GMA: DM or impaired fasting glucose), and patients without. PCT features and PCT and DM risk factors were retrieved from clinical charts and compared between groups. We identified 33 patients (41%) with GMA, of whom 27 (82%) developed GMA a long time after the diagnosis of PCT (mean 12·7 years). In bivariate analysis, these patients had significantly higher mean serum ferritin at diagnosis (651 vs. 405 ng mL(-1); P = 0·005), a higher prevalence of persistently elevated serum ferritin (52% vs. 15%; P < 0·001 for trend) and a higher prevalence of family history of DM (48% vs. 19%; P = 0·004). In multivariate analysis, persistently elevated serum ferritin [odds ratio (OR) 10·66, 95% confidence interval (CI) 1·95-58·19; P = 0·006] and family history of DM (OR 4·82, 95% CI 1·34-17·33; P = 0·016) remained significantly associated with the presence of GMA. GMA are highly prevalent in patients with PCT and mostly develop a long time after the diagnosis of PCT. Persistent hyperferritinaemia seems to be a risk biomarker of GMA in patients with PCT, probably in the setting of chronic iron overload and hepatic inflammation. Strict long-term monitoring of glucose metabolism and serum ferritin may be advisable in the routine follow-up of patients with PCT.