Rare association of insulin autoimmune syndrome with ankylosing spondylitis

Summary

Insulin autoimmune syndrome (IAS) is a rare cause of hyperinsulinemic hypoglycaemia, which is known to occur in association with the use of sulfhydryl-containing drugs and autoimmune disorders. We describe a patient with hitherto an unreported association of IAS with ankylosing spondylitis. We have also performed and described a simplified method of polyethylene glycol (PEG) precipitation of an insulin bound antibody in the serum.

Learning points

• IAS should be considered in differential diagnosis of endogenous hyperinsulinemic hypoglycaemia.

• Ankylosing spondylitis can be associated with IAS apart from several other autoimmune diseases.

• Very high serum insulin levels (100–10 000 μU/ml) are frequently seen in IAS.

• When faced with very high serum insulin before suspecting insulinoma, it is advisable that PEG precipitation of serum be done to identify antibody bound insulin.

• A clinical suspicion of IAS can avoid expensive imaging and unnecessary surgery in affected patients.