Comorbidity between CIDP and diabetes mellitus: only a matter of chance?

Background and purpose: It is well known that chronic inflammatory demyelinating polyneuropathy (CIDP) and diabetes mellitus (DM) are often associated, but it is not clear if these two disorders are patogenetically correlated. Methods: An epidemiological study on CIDP in two Italian regions (population 4 334 225) was performed, using multiple concurrent sources of cases. The presence of DM was assessed on basis of the data reported in the clinical records of each patient. Standardized morbidity ratio (SMR) was calculated, using as reference the prevalence of DM in northern Italy. Results: At the prevalence day 155 patients with CIDP resident in Piemonte and Valle d’Aosta were found. Of these, 14 were also affected by either type 1 or type 2 DM. The number of expected individuals with associated DM was 13.03, corresponding to a SMR of 1.07 [95% confidence intervals (CI), 0.58–1.80]. Patients with CIDP associated with DM had a higher level of CSF proteins and a longer delay from onset to diagnosis than patients without DM, but did not differ for age of onset, gender distribution, and type of clinical course. Conclusions: Our epidemiological findings do not support a pathogenetic correlation between DM and CIDP.