Insulin Injection Site Lipohypertrophy

Insulin injection site lipohypertrophy is a localised, rubbery thickening of subcutaneous fat at sites of repeated insulin injection or infusion. It causes variable insulin absorption and unexplained glycaemic swings.

It is common, reported in roughly one third to one half of insulin treated people.

Risk factors are failure to rotate sites, repeated injection in a small area, needle reuse, long insulin treatment, higher doses and use of the abdomen or thigh.

Pathophysiology.

Insulin is a local anabolic stimulus for adipocytes. Repeated injection into the same tissue causes hypertrophy and fibrosis.

Absorption from these sites is delayed and erratic. Injecting into normal tissue after rotation can cause sudden hypoglycaemia.

• Soft, rubbery or firm swelling, sometimes visible only on palpation.
• Unexplained hyperglycaemia or glycaemic variability, high insulin dose requirement and unexplained hypoglycaemia after a change of site.

• Inspect and palpate all injection sites at least yearly and at each visit if control is erratic, with good light and the patient standing. Ask where each insulin is injected.
• Ultrasound if clinical examination is uncertain.
• Review glucose or sensor data for variability that settles after a site change.

Differential diagnosis.

• Lipoma.
• Localised insulin derived amyloid mass (firm; Congo red positive on biopsy).
• Haematoma, abscess or injection site reaction.
• Lipoatrophy (opposite) and rarely soft tissue tumour.

• Stop injecting into affected areas until the tissue normalises (often months).
• Rotate within a map of sites, spacing injections at least 1 cm apart, and use a new needle each time (4 mm pen needles).
• When switching to normal tissue, reduce the insulin dose by about 10 to 20% initially and titrate to glucose, with some needing larger reductions and close monitoring for hypoglycaemia.
• Pump users: change infusion set every 2 to 3 days and rotate sites.
• Rarely, liposuction or excision for severe or persistent masses.

Monitoring. Check glucose at least 4 times daily after a site change for 2 to 4 weeks, and examine sites at each visit.

Referral and escalation. Diabetes educator for injection technique. Surgical review if a mass persists despite rotation or amyloid is suspected.