INS and type 2 diabetes mellitus: This case report aims to present the first documented evidence of isolated hypoglycemic brain injury inducing transient, profound diarrhea through a hypothesized brain-gut pathway, in a patient with all confounding factors rigorously excluded and premorbid normal gut histology.<h4>Patient concerns</h4>A 65-year-old male with type 2 diabetes suffered an insulin overdose, resulting in profound hypoglycemia (glucose 1.8 mmol/L) and a 10-minute comatose state.