The term “back mice” is a rather cute description for a painful yet often overlooked condition, even by back pain specialists. The term “back mice” was first used to label the condition by Peter Curtis in 1993. Back mice present as small, firm, fleshy yet moveable nodules upon palpation over the sacral region. Firm pressure directly on the nodules usually produces pain and tenderness, which sometimes radiates into the sacrum and hip. Also, the back mouse seems to suddenly appear following trauma to the back as in a motor vehicle accident or perhaps following a lifting injury. The size of the nodules does not change and they remain the same regardless of the administered soft tissue treatment.
Perhaps a more descriptive term for the back mouse is “lumbar fascial fat herniation” . This occurs when the lumbar subfascial fat layer herniates through the overlying thoraco-dorsal fascia and gets trapped and inflamed. The mechanism appears to be due to an anatomical defect or weakened area in the fascia, which, when there is increased internal pressure, allows the fat lobules to push through the fascia. Once herniated, the fat becomes trapped and as an expanded, inflamed, herniation in an otherwise unyielding fibrous capsule. This creates a focus of pain. Pressure on the fat mouse does not push it back through the fascia but only inflames the torn fascia more. These herniations occur at predictable sites along the iliac crest and sacrum very close to the natural dimple area. They also are approximately three times more prevalent in women, particularly in moderately obese women.
A client usually presents with an episode of low back pain. There may be a history of pain with lifting or prolonged sitting and the pain is usually greater on one side more than the other. The pain may radiate into the buttocks and sacrum and perhaps to the lateral thigh and into the lower extremity. Medications usually do nothing. Many will have gone through the pain pill merry-go-round, taking a cocktail of pain and anti-inflammatory medications even though the pain never truly goes away. The client has often tried everything, been everywhere and you are their last hope. They may have had radiographs, MRI studies or nerve conduction studies, all with negative or minimal findings. They may even have a minor disc bulge without nerve compression, yet the pain exactly mimics a discogenic disorder. When asked to point to the area of the greatest pain, they will invariably point just above and lateral to the natural “dimple” where the back and buttocks come together, near the multifidis triangle. When the area is palpated, the most marked finding is one or several firm, mobile 1.3 cm nodules. When pressed, these nodules reproduce the client’s complaints of back pain as well as the “sciatic” pain.
Subcutaneous lipomas in the back region differ from back mice in that they present as moveable non-tender “speed bumps” that cause pain only when they compress the underlying soft tissue. Subcutaneous lipomas can be found anywhere in the body. They grow slowly over time and are only cosmetically important.
Fig 2. Overlying thoraco-dorsal fascia.
Fig 3. Iliac crest and sacrum.
There always seems to be a focus by back pain specialists upon the disc and nerves issues even though the fat mice are readily palpable. Many sufferer’s have had epidural injections without success. I have had clients who have had surgery for disc herniations yet who still point to the back mouse post surgery as the focal point of pain. It could perhaps be considered diagnostic for the presence of a lumbar fascial fat herniation if a local infiltration of anesthetic takes away the pain.
A medical doctor can inject the back mouse with a local anesthetic. This usually only helps temporarily. Dry needling techniques by acupuncturists may help reduce the tension in the fibrous capsule. Good results may sometimes be obtained with local electrical stimulation techniques such as electro-acupuncture. Do not apply deep pressure to back mice during manual physiotherapy treatment. Doing so may only serve to aggravate the herniation. Release of muscular tissue tension around the back mouse may provide some relief by easing pressure on the area.
Perhaps the only permanent cure for the back mouse is its excision and removal. This could be performed by a hernia repair specialist. Once the fat herniation is excised and the fascial tear repaired, the client usually enjoys a more enduring and sometimes dramatic relief. One of the biggest problems is that so many medical doctors fail to recognize this condition; they tend to discount its existence, thereby limiting the treatment options. Icing the area may also provide temporary relief.
For a short video on back mice click here.
Physiotherapist in Tralee. Phone 0867700191 to discuss your injury, make an appointment or get a second opinion.
