Rabson-Mendenhall Syndrome Nearly Misdiagnosed as Type 1 Diabetes Mellitus: A Case Report.

Rabson-Mendenhall syndrome (RMS) is a rare genetic condition marked by severe insulin resistance, leading to persistent hyperglycemia that can sometimes be misdiagnosed as type 1 diabetes mellitus (T1DM). This case report details a 34-year-old male who was referred to a tertiary center for genetic evaluation to rule out insulin resistance syndrome. The patient had been diagnosed with T1DM since childhood, struggling to control his hyperglycemia despite high doses of insulin. Physical examination revealed acanthosis nigricans, prognathism, and other dysmorphic features. Genetic testing identified pathogenic variants in the insulin receptor (INSR) gene, confirming the diagnosis of RMS. Insulin resistance syndromes are prone to misdiagnosis, so a thorough patient history and careful physical examination are essential in distinguishing T1DM from insulin resistance syndrome. This is the first documented case of RMS in Saudi Arabia, and we emphasize the clinical findings and genetic confirmation in this patient.