What You Need to Know About Back Mice (Including the Best Treatment)

Back mice are painful masses of fat in and around the hips, the end of the spinal column (sacrum), and lower back. Depending on their cause and severity, treatment options may include self-care, alternative therapies, and medical treatments such as surgery.

"Back mice" is a non-medical term that refers to fat growths caused by several conditions. The masses are also known as subfascial fat herniation or episacroiliac lipoma.

What Are Back Mice?

"Back mice" is a term that usually refers to painful lumps of fat (lipomas), usually on the lower back. However, it can also be used to describe fibrous tissue or other types of nodules in this location.

In some cases, back mice protrude (herniate) through the lumbodorsal fascia, the network of connective tissue that covers the deep muscles of the low and middle back. Subcutaneous back mice develop in the tissue under the skin.

Causes

Back mice can be a result of many different co-occurring conditions that can lead to their formation. These conditions include:

• Iliac crest pain (or iliolumbar) syndrome: This condition develops when there is a tear in the iliolumbar ligament, the band that connects the fourth and fifth lumbar vertebrae with the ilium on the same side. It's usually the result of tearing or trauma to the iliolumbar ligament, due to repeated bending and twisting, a fall, or an accident.
• Multifidus triangle syndrome: This condition develops when the multifidus muscles along the spine become impaired. These muscles can atrophy (shrink) and intramuscular fatty tissue replaces the muscle, making the spine less stable and causing lower back pain.
  
• Lumbar fascial fat herniation: This is a painful mass of fat that protrudes through the lumbodorsal fascia—a thin, fibrous membrane that covers the deep muscles in the back. The herniation gets trapped and becomes inflamed, causing pain. The cause of this type of herniation is unknown.
• Lumbosacral fat herniation: This type of painful mass occurs in 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: This 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 the back muscles in place).
  

Symptoms

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

Signs of back mice include:

• Lumps under the skin that move when poked
• Pain, resulting from pressure being placed on the lump

Back mice can often be seen under the skin and may feel firm or rubbery. 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.

Diagnosis

An abnormal fatty growth should always be evaluated by a dermatologist or other healthcare provider. In addition to asking you questions about your health history and when you first noticed the mass, a healthcare provider will feel the back mice and examine the skin surrounding it.

A physical exam may provide enough information to diagnose a lipoma. However, sometimes imaging and laboratory tests are done. These may include:

• X-ray
• Computerized tomography (CT) scans
• Magnetic resonance imaging (MRI) scans
• Biopsy
  

Treatment

Back mice are usually benign (non-cancerous), so there's usually no reason to remove them. Your healthcare provider may recommend taking a watchful waiting approach—coming in regularly for exams to monitor the mass for any changes.

Treatment to manage back mice may include:

• Self-care: Applying heat or ice to the area may help to relieve some of the pain associated with back mice. You also can avoid wearing tight clothing or fabrics that irritate the site.
• Massage: Some studies suggest that deep tissue massage can bring pain relief and improved function, at least for several days following treatment sessions. Due to the hard-to-reach location of back mice and the importance of technique, professional therapy may be needed.
• Pain relievers and anti-inflammatory drugs: 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.
• Acupuncture and dry needling: 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 study reported that the anesthetic injections followed by dry needling (similar to acupuncture) improved pain relief.
• Surgery: Back mice are removed when they cause severe pain or interfere with daily activities. This surgical procedure involves cutting out the mice and repairing the surrounding fascia. It's not uncommon for back mice to return, however.
• Liposuction: If the back mice are smaller, more extensive, and contain more fluid, liposuction may be effective.

Additional treatments under study include yoga, vibration therapies, and ultrasound-guided manual techniques. Electrical stimulation also shows promise in treating back mice pain.

Differential Diagnosis

The fatty deposits can have a range of causes, as do the sources of nerve pain. Apart from back mice, your healthcare provider may need to consider and rule 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
• Adiposis dolorosa: Commonly known as Dercum's disease, this is a rare condition of painful subcutaneous adipose (fat) tissue that can include lumps of various sizes. These lumps occur in various places on the body and pain can be severe when pressed. Some other forms of adiposis dolorosa include familial multiple lipomatosis and Madelung’s syndrome.

Painful lipomas are also can occur 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) scans may be done to find the exact location of the nodule.

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.