Insulin Deficiency Metabolism
Overview
Insulin is the central anabolic hormone governing glucose, fat, and protein metabolism. Its deficiency — absolute in Type 1 DM, relative in Type 2 — leads to unchecked catabolism, hyperglycaemia, and, in the extreme, Diabetic Ketoacidosis (DKA).
Anabolic Effects of Insulin (Lost in Deficiency)
- Glucose disposal: Insulin promotes GLUT-4 uptake in muscle and adipose tissue. Deficiency = persistent hyperglycaemia.
- Glycogen synthesis: Stimulates hepatic glycogen synthesis and inhibits glycogenolysis. Deficiency = enhanced glycogenolysis.
- Protein synthesis: Promotes amino acid uptake and inhibits protein catabolism. Deficiency = muscle wasting.
- Lipid storage: Stimulates lipoprotein lipase in adipose tissue. Deficiency = lipolysis, elevated FFAs → ketogenesis.
Diabetic Ketoacidosis (DKA)
The classic triad: Hyperglycaemia + Ketosis + Metabolic Acidosis. Absolute insulin deficiency with high counter-regulatory hormones (glucagon, catecholamines) causes unrestrained hepatic gluconeogenesis and fatty acid oxidation to ketone bodies.
WarningCerebral Oedema in DKA
Cerebral oedema is the most feared complication of DKA treatment, especially in children. It is thought to occur from rapid osmotic shifts when plasma glucose falls too quickly with aggressive fluid/insulin therapy. CT shows diffuse cerebral swelling, sulcal effacement. Treat with IV mannitol.
Imaging Complications of Diabetes
- Infective Causes: Emphysematous pyelonephritis (gas in renal parenchyma), rhinocerebral mucormycosis (rapid sinus and orbital invasion on MRI), Fournier's gangrene.
- Vascular: Peripheral arterial disease (calcified medial calcinosis on plain film), diabetic nephropathy (bilateral enlargement early, then small shrunken kidneys).
- Neuropathic: Charcot arthropathy (disorganised, 'bag of bones' foot on X-ray).
High Yield Facts
LightbulbFRCR / MD Prep Pearl
Emphysematous pyelonephritis: gas within the renal parenchyma (distinct from collecting system gas). Almost exclusively in diabetics and immunocompromised patients. CT is the diagnostic gold standard. Class I/II (gas limited to parenchyma) can be managed with IV antibiotics + drainage; Class III/IV (perirenal/peritoneal extension) requires emergent nephrectomy.