The condition is called lipohypertrophy, which is an abnormal accumulation of fat beneath the skin. It literally means enlargement (hypertrophy) of fat cells (lipo). Lipohypertrophy is most common in people who receive frequent, multiple daily injections of insulin or use an insulin pump.
The hard bumps, usually found at injection sites, are an accumulation of fat and may also contain some scar tissue. Sethu Reddy, M.D., Chief of the Adult Diabetes Section at the Joslin Diabetes Center, explains that lipohypertrophy occurs when a patient uses the same injection site too often. Insulin acts on fat cells and encourages fat accumulation. “When fat cells get exposed to a lot of insulin they get happier and they get bigger,” says Dr. Reddy.
However, there may be other contributing factors as well. Lipohypertrophy is more common in people with type 1 diabetes than those with type 2, though researchers are still unsure exactly why. A patient’s unique skin sensitivity may also play a role.
Unfortunately, individuals may seek out these lipohypertrophic sites for injections since they tend to be less painful than at other sites. Not only does this make the lumps bigger, it can interfere with insulin therapy. The absorption of insulin can be erratic from these sites. Often, insulin absorption is delayed, leading to initial high blood sugars but later unexpected hypoglycemia. Lipohypertrophy itself is not life threatening, but it can make diabetes disease management more difficult.
The best way to avoid abnormal tissue accumulation is to rotate your injection sites and use as much of the skin surface as you can, over the course of weeks or a month.
“When we tell patients to rotate their injection sites, they might interpret that as right side then left side, then right side again and so on,” says Dr. Reddy. “So I tell people to think of the abdomen not just as two spots, left and right, but as a whole big map. And you can use any part of that map for an injection.”
Dr. Reddy also emphasizes the importance of rotating insulin pump injection sites as much as possible. “It’s a bit of a challenge,” says Dr. Reddy, “But since they keep that needle in for sometimes three days at a time, folks on pump therapy are much more likely to develop lipohypertrophy.”
If you are using your abdomen to inject, be sure to inject about an inch or two away from your last site. Mixing up your injections into a memorable pattern can also help you consistently rotate your site. You should also use a fresh needle each time. You can use a logbook, phone apps, or even tiny temporary tattoos to help you keep track.
If you have Lipohypertrophy
If you find yourself developing lumps and bumps beneath your skin, try to avoid injecting in the same place for two weeks to three months (depending on the size of the lumps). “If you catch the small lumps early they can eventually regress,” says Dr. Reddy. “But if the lump develops over the course of years you could end up with something the size of a grapefruit.”
Dr. Reddy explains that even though large lumps aren’t usually painful, many patients find them unsightly. Severe lipohypertrophy can be treated with liposuction or minor cosmetic surgery.
If you’re switching up your injection spots, keep in mind that different places on your body absorb insulin differently. In general, your abdomen absorbs injected insulin the fastest. After that, your arm absorbs it most quickly. The thigh is third fastest area for absorption, and the buttocks absorb insulin at the slowest rate. If you’re concerned about a fluctuation in your insulin uptake, talk to your doctor about temporarily adjusting your insulin dosing.
If you regularly rotate your injection site but still find the hard lumps associated with lipohypertrophy, consult with your doctor or dermatologist. There may be something else going on.
Make it a habit to routinely inspect your injection sites for signs of lipohypertrophy. Early on, you may not see the bumps, but you’ll be able to feel the firmness under your skin. You may also notice that the area is less sensitive and you feel less pain when you inject. The fastest way to get rid of the lumps is to catch them when they’re small, so do a quick check once a week to make sure your skin feels normal.
“Lipohypertrophy is not an allergic reaction,” says Dr. Reddy. “Insulin promotes fat and the development of fatty lumps is expected. It’s just something to watch out for and it can definitely play havoc with your sugar control.”