Understanding Back Mouse, aka Episacroiliac Lipoma

Often misdiagnosed, pain relief from back mice can be illusive

Back of the pelvis including sacroiliac area.
Back of the pelvis including sacroiliac area. SCIEPRO / Getty Images

Back mouse is a condition characterized by painful bumps in and around the hips, sacrum and low back. Accurately diagnosing it is often a stumper for doctors and other health practitioners. Because of this, carefully considering the treatment recommendations you are offered (should you find yourself with these painful nodules) is absolutely key to getting better.

Let's sort out the known facts to give you a reference for dealing with this back problem effectively.

Overview

Back mice have been known to surgeons since 1937 when Reis reportedly named them episacroiliac lipoma. Since then, a number of names have been attributed to this condition including: Iliac crest pain syndrome, multifidus triangle syndrome, lumbar fascial fat herniation and lumbosacral fat herniation.

Many authors believe that of all the terms used to identify back mouse, the last two—lumbar fascial fat herniation and lumbosacral fat herniation—are the most accurately descriptions.

A back mouse is a fat mass that protrudes abnormally through the lumbodorsal fascia. The lumbodorsal fascia is a big diamond-shaped sheath of connective tissue located in the lumbar (low back) and thoracic (mid-back) areas of your back. Back mice also occur in the hip bones in back, as well as the sacroiliac region.

Symptoms

Now, you might think that a simple fat mass couldn't cause much pain, but in this case, at least, that's not so.

Patients (and their surgeons) often report excruciating pain due to back mice. Along with the pain, telltale symptoms may include visibly notable nodules in the low back and sacral areas, and, when the nodules are touched or pressed, a reproduction of the type of pain that likely drove you to seek (or consider seeking treatment in the first place.

Very few research studies have been conducted on the topic of back mice, and that may explain why so little is know about it in the spine care profession. Articles written online by chiropractor David W. Bond provide the most comprehensive information available on this subject.

Bond reports that moderately obese women seem to be at a higher risk for back mice than others. He also says that often people with back mice quite often go through a battery of treatments with, unfortunately, no pain relief to show for it.

Diagnosis and Treatment

One way to diagnose back mice is by injection (or surgery). If injecting a local anesthetic relieves the pain—albeit temporarily—the diagnosis is suggested. Case studies from the 1940s show that when back mice are surgically removed, this almost always fully relieves the pain.

Currently, surgery (excision of the mice, followed by repair of the fascial openings through which they emerged) appears to be the only way to achieve durable pain relief from back mice. The problem is, often hundreds of back mice may be present, which complicates achieving full pain relief using this method. That said, Bond, who is a chiropractor, believes this condition may be successfully treated by combining acupuncture and spinal manipulation.

A 2016 medical case study and review of literature found that injecting a local anesthetic or steroids into the nodules, followed by dry needling may lead to pain relief. The same study found just one clinical trial comparing an injection of local anesthetic to a saline solution. In this study the injections were not followed by dry needling, and patients reported only mild and fleeting pain relief.

Similar Conditions

Sciatica 

As I mentioned above, it's not uncommon for doctors to misdiagnose back mice. And sciatica is the most common misdiagnosis they settle on. Why? What's the correlation between back mouse and pain and other symptoms that go down one leg?

While pain from back mice starts locally, at the nodules themselves, it often, like sciatica, radiates to other areas. Like sciatica, back mouse pain tends to be unilateral, and can increase depending on your position. The pattern of pain radiation is generally not uniform.

Bond says that irritation that comes from back mouse doesn't show up on nerve root tests — unless you also have a herniated disc. He adds that the condition may be accompanied by spasms in your paraspinal muscles, as well as decreased lumbar range of motion. Pain intensity can vary, as can how long it lasts (duration.)

Trigger Points

While it's possible to pinpoint back mouse pain and/or tenderness by touching one of the critters, back mice are not trigger points. Trigger points present themselves as taut bands muscle while back mice are felt as masses or nodules.

Back mice are not tight muscles, either, so pressing down on them will not contribute to their cure or management. In fact, this kind of treatment causes pain, Bond says. This means that a deep massage will likely not be the correct treatment.

Sources:

Bicket, M. The Best-Laid Plans of "Back Mice" and Men: A Case Report and Literature Review of Episacroiliac Lipoma. Pain Physician. March. 2016.

Denman C. Hucherson, M.D., Joe R. Gandy, M.D., Herniation of fascial fat: A Cause of Low Back Pain. The American Journal of Surgery. November 1948.

Bond, D. Chiropractic Treatment of the Back Mouse. Dynamic Chiropractic. September 2004. http://www.dynamicchiropractic.com/mpacms/dc/article.php?id=46427

Bond, D. Low Back Pain and Episacral Lipomas. Dynamic Chiropractic. September 2000. http://www.dynamicchiropractic.com/mpacms/dc/article.php?id=31867

Rosati E, Mariani D. The role of episacroiliac lipomas as a cause of pseudolumbago-sciatica syndromes. Arch Putti Chir Organi Mov. 1990.

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