Skeletal Muscle Mass and Body Weight Fall Proportionally With Use of Dual Glucagon-Like Peptide 1/Glucose-Dependent Insulinotropic Polypeptide Receptor Agonist Tirzepatide: Case Report and Review of Literature.

OBJECTIVE: Multiple studies have demonstrated that treatment with tirzepatide results in significant improvement in HgbA1c as well as meaningful weight loss. Although the loss of skeletal muscle mass has been well described with the use of glucagon-like peptide 1 receptor agonists, there is little information regarding the effect of dual glucagon-like peptide 1/glucose-dependent insulinotropic polypeptide receptor agonist tirzepatide on skeletal muscle mass. METHODS: We performed serial body composition measurements in a 68-year-old male who presented with a body mass index of 31.2 kg/m2 and hemoglobin A1c of 5.9%. Treatment with tirzepatide resulted in a reduction of weight by 28.7 lbs, a decrease in body mass index to 26.8 kg/m2, and normalization of A1c (5.3%). The patient, however, also experienced a 9.9 lb loss of skeletal muscle mass, which was proportionate to a reduction in body weight - approximately 15% from the initial value for both. Muscle mass loss constituted 34% of the total body weight loss. RESULTS: To our knowledge this is the first report of multiple serial body composition measurements in a patient on treatment with tirzepatide. The time course and the magnitude of the loss of body weight, fat mass and skeletal muscle mass are detailed. CONCLUSION: We propose that, in addition to weight measurements, serial body composition assessments should be obtained in patients on tirzepatide. If this is not available, our findings suggest that, at least in some cases, the percent of muscle mass lost is similar to the percent reduction of total body weight.