Back Mice Symptoms, Diagnosis, and Treatments

"Back mice" is a non-medical term used to describe painful masses of fat in and around the hips, the end of the spinal column (sacrum), and lower back. The term is used by some—chiropractors, in particular—to describe several different conditions.

Some professionals argue against calling such bumps "back mice" because the term is not specific. The concern is that it may lead to misdiagnoses or incorrect treatment.

This article looks at what back mice are, the conditions linked to them, their symptoms, and how they're diagnosed and treated.

What Are Back Mice?

"Back mice" is a nonspecific term that refers to painful lumps of fat (lipomas), fibrous tissue, or other types of nodules located on the back, usually the lower back. In some cases, they protrude (herniate) through the lumbodorsal fascia. This is the network of connective tissue that covers the deep muscles of the low and middle back. Others may develop in the tissue under the skin (subcutaneous).

Back mice were first described in medical literature in 1937 when healthcare provider Emil Reis used the term in association with a condition called episacroiliac lipoma.

Since then, many conditions have been associated with back mice. These include:

• Iliac crest pain syndrome
• Multifidus triangle syndrome
• Lumbar fascial fat herniation
• Lumbosacral fat herniation
• Episacral lipoma

Most often, the term describes lipomas.

Related Conditions

The following conditions are associated with back mice.

Iliac Crest Pain Syndrome

Also called iliolumbar syndrome, iliac crest pain syndrome develops when there is a tear in the iliolumbar ligament. This band of ligament connects the fourth and fifth lumbar vertebrae with the ilium on the same side.

Causes of iliac crest pain syndrome include:

• Tearing the iliolumbar ligament due to repeated bending and twisting movements
• Trauma or fracture of the ilium bone due to a fall or car accident

Multifidus Triangle Syndrome

Multifidus triangle syndrome develops when the multifidus muscles located along the spine become impaired. These muscles can atrophy (shrink) and intramuscular fatty tissue replaces the muscle. Atrophied muscles make the spine less stable and cause lower back pain.

Lumbar Facial Fat Herniation

Lumbar fascial fat herniation is a painful mass of fat that protrudes through the lumbodorsal fascia—a thin, fibrous membrane that covers the deep muscles in your back. This herniation get trapped and inflamed, causing pain.

It isn't known what causes the herniation to occur.

Lumbosacral Fat Herniation

Similar to lumbar fascial fat herniation, lumbosacral fat herniation is a painful mass that occurs in a slightly different location. Lumbosacral describes the area where the lumbar spine meets the sacrum (five fused vertebrae that form one single bone).

It isn't known what causes the herniation to occur.

Episacral Lipoma

Episacral lipoma is a small, tender nodule under the skin primarily occurring over the top, outer edges of the pelvic bone.

These painful lumps occur when a portion of the dorsal fat pad pokes through a tear in the thoracodorsal fascia (the connective tissue that helps hold your back muscles in place).

For this particular lipoma, your healthcare provider may refer you to an orthopedist or orthopedic surgeon. You also may get pain relief from a massage therapist who's familiar with the condition.

Back Mice Symptoms

Back mice lumps can often be seen under the skin. They are typically tender to touch and can make it hard to sit in a chair or lie on your back, since they often appear on the hip bones and sacroiliac region.

Back mice:

• Feel firm or rubbery
• Will move under your skin when poked
• Form unsightly lumps
• Cause excruciating pain

The pain associated with back mice results from pressure being placed on the lump, which compresses the nerves. Damage to the underlying fascia can also cause pain.

Diagnosis

Some people do not realize they have lumps until pressure is exerted on them. In fact, back mice are often found by chiropractors and massage therapists during routine treatments.

Determining what these lumps are can be difficult. Because they are non-specific, healthcare providers sometimes diagnose back mice by injecting a lump with a local anesthetic. If it relieves the pain, the lump is likely a back mouse.

This way of making a diagnosis can be problematic. Giving a local anesthetic, by its nature, will relieve nerve sensations and, therefore, pain. So, such a result is proof of pain but not necessarily the pain's cause.

Differential Diagnosis

The fatty deposits can be any number of things, some serious and others not. The same applies to the sources of nerve pain.

While a lipoma/back mouse is the most obvious explanation, your healthcare provider may finalize diagnosis by ruling out other causes such as:

• Sebaceous cysts: A benign, fluid-filled capsule between layers of skin
• Subcutaneous abscess: A collection of pus beneath the skin; often painful, may become red or inflamed
• Sciatica: Radiating nerve pain down one or both legs caused by a herniated disc or a bone spur in the lower back
• Liposarcoma: Malignant tumors that sometimes appear as fatty growths in the muscles

Painful lipomas are also associated with fibromyalgia, a chronic condition that involves abnormal pain signals.

Most of these conditions are diagnosed simply by doing a physical exam and taking a medical history. However, liposarcoma is typically diagnosed by doing a biopsy where some tissue is removed from the nodule and examined under a microscope for cancer cells. Magnetic resonance imaging (MRI) or computed tomography (CT) scan may also be done to find the exact location of the nodule.

Treatment of Back Mice

Back mice are usually benign, so there's no reason to remove it unless it's causing pain or making it difficult to move. It should be checked, though, to make sure it's not cancerous.

Treatment usually involves injected anesthetics, such as lidocaine or corticosteroids. You can also try over-the-counter pain relievers such as non-steroidal anti-inflammatory drugs.

If pain is severe, surgical removal may be possible. It involves cutting out the mice and repairing the fascia. This is the only known way to get lasting pain relief.

However, if you have a lot of back mice—some people have hundreds—removal may not be a good option. If the back mice are smaller, more extensive, and more fluid, liposuction may be effective.

Complementary and Alternative Treatment

Many chiropractors believe that back mice can be successfully treated with complementary and alternative (CAM) therapies. A common approach uses acupuncture and spinal manipulation. It's less invasive than standard treatments and is unlikely to harm you.

A 2016 case study reported that the anesthetic injections followed by dry needling (similar to acupuncture) improved pain relief.

Summary

Back mice are fatty lumps under the skin that cause pain by compressing nerves and damaging your fascia. They move if you press on them and mostly show up in the lower back and hip area.

Diagnosis can be made by injecting an anesthetic and seeing if the pain goes away. Treatment may involve more injections or surgery if pain is severe and doesn't go away. CAM treatments like acupuncture, dry needling, and spinal manipulation may help.