Co-existence of Type 1 Diabetes Mellitus and Myasthenia Gravis: A Case Report and Review of the Literature

Type 1 diabetes (T1D) and myasthenia gravis (MG) are autoimmune conditions that rarely co-occur. Here, we report a child with MG who subsequently developed T1D. An 11-year-old girl with seropositive MG diagnosed at 4 years of age presented with muscle pain, cramps, and weight loss of 3.5 kg over 4 months. Her MG was in remission on daily pyridostigmine. She denied polyuria, polydipsia, recent illnesses, or other medications. She was prepubertal and had stable vitals with normal systemic examination. Initial work up for a probable diagnosis of rhabdomyolysis showed hyperglycemia and glucosuria. She had ketosis without acidosis. Diabetes autoantibodies were positive (anti-glutamic acid decarboxylase antibody 113.5 IU/mL (reference range < 5 IU/mL), anti-zinc transporter 8 antibody > 500 U/mL (reference range < 15 IU/mL)). Screening for autoimmune thyroid disease and celiac disease was negative. Patient was diagnosed with T1D and was started on subcutaneous insulin. The co-existence of MG and T1D is rare. All the 4 prior reported patients from Europe were diagnosed with T1D prior to or concurrently with MG. In contrast, our patient was first diagnosed with MG and subsequently diagnosed with T1D 7 years later. Consider screening for T1D in patients with MG and offering treatment to those above 8 years and older with stage 2 T1D to delay its onset. Along with other causes, T1D should also be considered when patients with MG present with nonspecific symptoms such as fatigue and weight loss.