Back mice is a nonmedical term used to describe painful lumps on or near the lower back and hips.

A 2016 article published inPain Physician describes back mice as “firm, rubbery, mobile nodules that are located in characteristic regions of the sacroiliac, posterior superior iliac, and the lumbar paraspinal regions.”

The term “back mice” was originally used in 1993 by Peter Curtis to describe a condition known as an episacral (or episacroiliac) lipoma. The term now refers to a number of different conditions.

Keep reading to learn more about back mice and what you can do about them.

Often diagnosed as nonspecific low back pain, back mice is a nonmedical term that could refer to many conditions, including:

Episacral lipoma

Episacral lipoma is a small, tender subcutaneous (under the skin) nodule. 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).

They primarily appear over the posterior iliac crest, which is the top, outer edges of your pelvic bone.

Iliac crest pain syndrome

Iliac crest pain syndrome, also known as iliolumbar syndrome, is the result of a tear in the iliolumbar ligament. This tear can occur if the iliolumbar ligament undergoes repeated bending motions or twisting actions.

It can also be caused by trauma, such as a fall, sports injury, or car accident.

Lumbar fascial fat herniation

Lumbar fascial fat herniation is a painful mass of fat that’s herniated (protruding) through the lumbodorsal fascia.

The lumbodorsal fascia is a thin, fibrous membrane which covers your back’s deep muscles.


A lipoma is an abnormal overgrowth of fat cells that form a lump under the skin. They are considered to be benign (noncancerous) tumors.

When a fatty deposit is found in the area of your lower back, the obvious answer tends to be lipoma. But some may refer to it as a back mouse.

Other conditions that may be called back mice are:

  • Sebaceous cyst. This fluid-filled capsule occurs within the skin (between the epidermal and dermal layers). Like lipoma, sebaceous cysts are benign.
  • Subcutaneous abscess. In this type of abscess, pus collects under the skin. Subcutaneous abscesses are often painful and, in later stages, become red and inflamed.
  • Liposarcoma. These malignant tumors can appear as fatty growths inside muscles.

Currently, treatment for back mice primarily consists of local injections of an anesthetic such as lidocaine and/or steroids.

A 2000 study indicated that 86 percent of participants were “satisfied” or “very satisfied” by a treatment consisting of an injection of local anesthetic and corticosteroid.

While the injections relieved local and radiating symptoms, they did not always eliminate the nodules. There were no reports of adverse events.

Back mice or a back mouse is a nonmedical term for painful lumps on your lower back or hips. Because it’s not a medical term, it may be used to describe a number of different conditions, including:

  • episacral lipoma
  • subcutaneous abscess
  • liposarcoma
  • Iliac crest pain syndrome
  • lumbar fascial fat herniation

If you have painful lumps on your hips or lower back, discuss the condition with a doctor. They can diagnose your condition and recommend a treatment plan.