title: The Best-Laid Plans of "Back Mice" and Men: A Case Report and Literature Review of Episacroiliac Lipoma.
abstract: 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.
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  Case report and literature review.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Anesthesiology, Critical Care, and Pain Medicine, Massachusetts General Hospital, Boston, MA.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Bicket
authors.affiliation: John Hopkins University, Baltimore, MD; 2Massachusetts General Hospital, Boston, MA.
authors.forename: Courtney
authors.initials: C
authors.lastname: Simmons
authors.affiliation: John Hopkins University, Baltimore, MD.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zheng
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007267:Injections; D008067:Lipoma / Q000150:complications / Q000000981:diagnostic imaging* / Q000188:drug therapy*; D017116:Low Back Pain / Q000000981:diagnostic imaging* / Q000188:drug therapy* / Q000209:etiology; D008875:Middle Aged; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging* / Q000187:drug effects
chemical_list: D000779:Anesthetics, Local