1. 2016;19;181-188The Best-Laid Plans of “Back Mice” and Men: A Case Report and Literature Review of Episacroiliac Lipoma
   Literature Review
   Mark C. Bicket, MD, Courtney Simmons, MD, and Yi Zheng, MD, PhD.

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.