As I understand it, the T3 label potentially covers a broad range of conditions:
(i) Type 3 has been applied to a condition where chronic insulin resistance and certain changes in brain chemistry have been noted in some patients that also have Alzheimer’s;
(ii) Type 3a relates to patients who show genetic dysfunction of pancreatic beta cells affecting or preventing production of insulin;
(iii) Type 3b relates to patients with a form of pancreatitis or another condition that has damaged or prevents production of digestive enzymes (so, not insulin production);
(iv) Type 3c relates to patients with a form of pancreatitis or another condition that has damaged or prevents both digestive enzyme production and Insulin production.
I am not a medical professional, but I do have T3c diabetes resulting from a gallstone impacted in my bile duct. All of the above info is based on my own research, so I’m happy to be corrected by anyone more knowledgeable than me. I hope this helps.