Interplay of diabetes mellitus and rheumatic diseases amidst the COVID-19 pandemic: influence on the risk of infection, outcomes, and immune responses.

Outcomes of COrona VIrus Disease-19 (COVID-19) in patients with rheumatic diseases (RDs) reported in various studies are heterogenous owing to the influence of age and comorbidities which have a significant bearing on the infection risk, severity, morbidity, and mortality. Diabetes mellitus (DM) and RDs are closely linked with underlying pathobiology and treatment of RDs affecting the risk for DM as well as the glycemic control. Hence, we undertook this narrative review to study the influence of DM on outcomes of COVID-19 in patients with RDs. Additionally, aspects of patient attitudes and immune response to COVID-19 vaccination were also studied. The databases of MEDLINE/PubMed, Scopus, and Directory of Open Access Journals (DOAJ) were searched for relevant articles. Studies from mixed cohorts revealed insufficient data to comment on the influence of DM on the risk of infection, while most studies showed twice the odds for hospitalization and mortality with DM. Specific cohorts of rheumatoid arthritis and systemic lupus erythematosus revealed a similar association. Poor health was noted in patients with spondyloarthritis and DM during the pandemic. The presence of DM did not affect patient attitudes towards vaccination and did not predispose to additional vaccine-related adverse effects. Immune response to inactivated vaccines was reduced but mRNA vaccines were maintained in patients with DM. Detailed assessment of DM with its duration, end-organ damage, and glycemic control along with a focused association of DM with various aspects of COVID-19 like risk, hospitalization, severity, mortality, post-COVID sequelae, immune response to infection, and vaccination are needed in the future. Key Points • Diabetes mellitus is associated with the severity of infection, COVID-19-related hospitalization, and mortality in rheumatic diseases across most studies but studies analyzing its specific role are lacking. • Poor outcomes of COVID-19 in RA and poor health in spondyloarthritis are strongly associated with diabetes mellitus. • Diabetes mellitus may negatively influence the humoral response to inactivated vaccines but does not seem to affect the immune responses to mRNA vaccines. • Diabetes mellitus does not influence the attitude towards vaccination or deviation from the prescribed medications during the pandemic.