Type 1 diabetes mellitus (T1DM) and multiple sclerosis (MS) have been described as chronic organ-specific diseases, approached by different medical specialties. However, they share more etiologic and pathologic features than expected between two autoimmune diseases. The authors present the case of a 40-year-old Caucasian male, diagnosed with type 1 diabetes mellitus at age 18, with poor metabolic control in the early years after the diagnosis. Fourteen years after the diagnosis of diabetes, he started complaining of paresthesias in both feet and sexual dysfunction. Months later, he began to have episodes of muscle weakness and decreased strength in the right lower limb, with a relapsing-remitting pattern and diplopia. This typical course of the symptoms associated with characteristic findings in brain magnetic resonance imaging, with multiple lesions, with evidence of space and time dissemination, established the diagnosis of multiple sclerosis. The presence of oligoclonal bands in the cerebrospinal fluid analysis sustained this diagnosis. Other alternative etiologies were excluded. People with type 1 diabetes mellitus are at an increased risk for other autoimmune diseases, with autoimmune thyroiditis (AIT), celiac disease, and pernicious anemia being the most common. Other less recognized associations, such as the co-occurrence of type 1 diabetes mellitus and multiple sclerosis, are also more frequent than might be thought, with studies reporting a threefold to fivefold higher prevalence of T1D in patients with MS. The exact mechanism behind this co-occurrence is not fully understood, but environmental factors (viral infections and vitamin D deficiency) and variations in non-human leucocyte antigen (HLA) class II alleles may be implicated. Understanding the similarities in the etiology and pathophysiology of these diseases may help clarify causality and create new strategies for the management of these conditions.
Keywords: autoimmune diseases; autoimmunity; genetic susceptibility; multiple sclerosis; type 1 diabetes mellitus.
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