Prevalence of lipohypertrophy in insulin-treated diabetic patients and predisposing factors.
Lipodystrophy is a well-known local complication of insulin injection that has two very different outcomes, causing either the swelling or the wasting of subcutaneous fat. These two reactions appear to have two different causes and mechanisms, lipohypertrophy (swelling) being caused by a cellular reaction to the local accumulation of insulin, and lipatrophy stemming from an immune reaction to impurities in the insulin. Lipohypertrophy is common in all diabetic populations, but tends to occur with particular frequency among children and young women. A group of German physicians assembled 223 type I (insulin-dependent) and 56 type II (non-insulin-dependent) diabetes patients in order to assess what caused the complication and suggest methods whereby it might be better prevented.
Researchers found that lipohypertrophy was far more common in the type I diabetics (28.7%) than in the type II diabetics (3.6%). Lipatrophy was far rarer; only 4.5% of all patients reported having suffered the condition. In the great majority of patients only one site was affected by lipohypertrophy, but the swelling was more commonly considered distinct (over 3 cm wide and 0.5 cm high) rather than discrete (smaller). Lipohypertrophy had first appeared in some patients when they were as young as five, in others as old as 48, but in the majority of subjects it had appeared between 15 and 30 years of age, and within five years of first using an insulin syringe or pen. The type of insulin used (human, porcine or bovine) did not affect the risk of lipohypertrophy.
Use of insulin pens appeared to increase the risk of lipohypertrophy compared with those patients who used only syringes; 35.7% of those who used only pens and 35.8% of those who used both pens and syringes developed the condition, while only 23.4% of those who never used pens showed signs of it. However, neither a higher number of daily injections nor larger daily doses of insulin meant a significantly increased risk of lipohypertrophy.
A myth surrounding this disorder is that patients cause and then aggravate lipohypertrophy by continually injecting into the same site because it is less painful. Under 22% of patients said that injection into the lipohypertrophic site was actually less painful, while over 23% found it more painful. For the remainder, there was no difference in sensitivity. However, the link between the condition and patients’ failure to rotate injection sites is real: 60% of those patients who always used the same injection site were afflicted, as opposed to only 22.1% of those who rotated regularly. Women were also almost twice as likely to suffer, and patients who used the abdomen as an injection site were also at greater risk. The upper arm, followed by the thigh, were found to be the safest places. More obese people, who naturally tend to have more subcutaneous fat, were at less risk than leaner people.
Previous studies have shown that children may be at particular risk. One 1993 survey at a summer camp for diabetic kids found that 45% had the condition. Lipohypertrophy is also quite common among young women with diabetes, and is frequently a cosmetic problem. Once it occurs, it is unusual for it to regress in the short term even if the injection site is no longer used. Fortunately, liposuction can be used to remove it. While improvements in insulin purity have greatly reduced the problem of lipatrophy in recent years, lipohypertrophy rates have barely changed. Patient education might achieve what science has not. Far simpler than surgery, and far better than waiting months or years for the swelling to disappear, is to avoid lipohypertrophy in the first place. The best way to do that is by rotating injection sites, particularly in the abdomen.