Background: Back mice, or episacroiliac lipoma, represent a potentially treatable cause of low
back pain that may be under-recognized in clinical practice. Despite being well characterized
based on clinical history and physical examination findings, implementation of appropriate
treatment may be delayed or missed based on a lack of familiarity with the diagnosis.
Objectives: In this case report and literature review, we describe a 47-year-old woman with
history of persistent low back pain who presented with a pain exacerbation consistent with a
back mouse. The history, epidemiology, clinical characteristics, differential diagnosis, potential
mechanisms for pain, and treatment options for back mice were then reviewed.
Study Design: Case report and literature review.
Setting: Academic university-based pain management center.
Results: Studies included one randomized clinical trial, 4 cross-sectional studies, 8 case reports
or series, and 16 other publications prior to 1967.
Limitations: A single case report.
Conclusions: Firm, rubbery, mobile nodules that are located in characteristic regions of the
sacroiliac, posterior superior iliac, and the lumbar paraspinal regions may represent fatty tissue
that has herniated through fascial layers. When painful, these back mice may be confused
with other causes of low back pain. In particular, the presence of point tenderness may mimic
myofascial pain, and reports of radicular pain may imitate herniated nucleus pulposus. However,
back mice may be distinguished from other entities based on findings from the history and
physical examination such as absence of neurological deficit. Treatment consisting of injection
of local anesthetic into the nodule with or without corticosteroid followed by repeated, direct
needling has been reported to relieve pain in many case reports. The one clinical trial comparing
injection of local anesthetic to normal saline, which did not include repeated needling, found
only mild and transient benefit in the treatment group.
Key words: Low back pain, back mice, back mouse, episacroiliac lipoma, lumbar subcutaneous
nodules, multifidus triangle syndrome, subcutaneous fatty nodes, case report, review
Sacral insufficiency fractures – a commonl y overlooked cause of low back and pelvic pain; a case report and literature review
