BACKGROUND: An association between porphyria cutanea tarda (PCT) and diabetes mellitus (DM) is widely reported, but the pathogenetic link remains unknown. OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.
BACKGROUND: An association between porphyria cutanea tarda (PCT) and diabetes mellitus (DM) is widely reported, but the pathogenetic link remains unknown. OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.