2016 Bicket

Bicket et al. emphasized the importance of CONSIDERING the epi-sacro-iliac lipoma or back mice as a CAUSE OF LOW BACK PAIN. They reviewed existing literature, including treatment options and presented a CASE REPORT. They finished saying that no recognizing back mice can lead patients to receive the INCORRECT DIAGNOSIS OF NON-SPECIFIC low back pain.

Notes about the article:

The Best-Laid Plans of “Back Mice” and Men: A Case Report and Literature Review of Episacroiliac Lipoma.

Bicket MC, Simmons C, Zheng Y.

Pain Physician. 2016 Mar;19(3):181-8. Review. PubMed PMID: 27008292.

Bicket et al. start with a mention to “low back pain problem

They start commenting that low back pain represents a common, costly and disabling condition. Still with unclear causes.

Low back pain patients have been categorized in 3 cohorts:

-nonspecific low back pain

-back pain associated with radiculopathy/spinal stenosis

-back pain associated with another specific spinal cause

They present a case report and a literature review that may help to describe one potentially treatable cause of back pain: “back mice

About epi-sacro-iliac lipoma or  “back mice”

Bicket et al. described “back mice” as palpable, freely movable, fatty tissue nodules found commonly in the sacroiliac region.

“Back mice” and other monikers

Back mice” have received various monikers over time: the most common of which is “episacroiliac lipoma” or (epi-sacro-iliac lipoma)

List of alternative names for back mice or epi-sacro-iliac lipoma:

-Episacral lipoma

-Sacroiliac lipomata

-Subcutaneous fatty nodes

-Lumbar subcutaneous nodule

-Tender rheumatic nodule

-Fibrositis nodule

-Multifundus triangle syndrome

-Iliac crest pain syndrome

Some notes about old references

-First description dates from 1935 from Sutro’s work.

-In the late 1930s and 1940s work with corpses was characterized by their occurrence’s pattern with nodules located in areas where fatty tissue herniates through fascial layers (especially Copeman and Ackerman’s work)

epi-sacro-iliac lipoma

-The areas correspond with: lumbar parespinal musculature, sacroiliac area and posterior superior iliac crest… but they have also been described in thoracic areas.

The name back mice

The sobriquet of back mice developed out of the need to communicate with patients about the mobile nature of the nodule, the rubbery consistency, and ABILITY TO CHANGE SIZE OVER TIME.

Bicket et al. CASE REPORT

epi-sacro-iliac lipoma

A 47-year-old woman with a 2-year history of persistent axial LOW BACK PAIN, with a 2-week period of exacerbation. No low extremities involvement. No trauma. The pain was described as intermittent, sharp, localized, bilateral in low back. Intermittent numbness. Pain triggers included twisting and walking. Soothing factors resting and laying down.

Physical examination revealed 2 mildly tender, distinctly palpable, freely movable nodules, measuring 4x2x3cm.

Deep palpation of nodules reproduced the patient’s sensations of pain as the numbness in posterior thigh.

The rest of examinations show no findings.

epi-sacro-iliac lipoma

They injected local anesthetic and corticosteroid under ultrasound visualization with no good response.

They repeated infiltration with a dry needling technique with good results after one month following up.


-The prevalence of these nodules is yet not clear since the result of the studies vary.

-The pain pattern that they present and the physical examination can help to differentiate from other etiologies.

-In comparison to myofascial trigger points, back mice lay superficial to muscle bands.

-Pain from back mice can radiate to leg, but there is absence of other neurological deficit, reflexes are intact, and no lack of sensory findings.

Back mice can give referred pains to the hip or the abdominal site.

-The injection and the repeated needling seem to be the best initial approach. Despite other studies focused on surgery that should be considered in case that injection does not give permanent relief. Despite sometimes pain persists even after surgery. Other described techniques have been radiofrequency or cryoablation.

-Nevertheless, the pain mechanisms of this entity are not yet clarified, pressure, tension or torsion have been suggested.

-They explained the only randomized trial of Collée that compared injection therapy with local anesthetic or with isotonic saline.

-Bicket et al. propose injection with local anesthetic and corticoisteroid with repeated needling as first treatment approach.

Published in May 2018 by Marta Cañis Parera   ORCID iD icon

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