Back mice visualized Using Magnetic Resonance?
Jensen and Degn emphasises that back mice is an important differential diagnosis in lower back pain. The diagnosis is typically based on clinical assessment with palpitation of painful freely moveable fatty nodules in the lumbar region. Back mice can be also visualized with musculoskeletal ultrasound. The authors’ main contribution is to present a patient with back mice treated with block injections, where the back mice were visualized both sonographically and for the first time with magnetic resonance imaging (RMI). Moreover, the authors suggest MRI as a diagnostic supplement in uncertain BM cases. (Personal note: for sure it is necessary more studies to determinate if these findings are common in all the cases).
Open Acces article: LINK
Notes on the article of:
Back Mice Visualized Using Magnetic Resonance Imaging in a Patient with Lumbar Back Pain
Jensen TSR and Degn J.
OMICS Journal of Radiology 2019; 8:310
Back mice visualized using magnetic resonance? Introduction by Jensen and Degn
- Jensen and Degn emphasise that the Lower Back Pain (LBP) is a common condition and the leading cause of years lived with disability worldwide.
- The LBP can be caused by several conditions, but in most patients, a specific pain-generator cannot be diagnosed, and the condition is defined as non-specific. However, in cases with a pathoanatomical pain-generator, correct diagnosis is crucial to initiate a targeted treatment.
- They explain that the Back Mice (BM) is single or multiple fatty nodules of variable size located especially in the lumbar region. BM is a cause of LBP which has been described in both clinical and surgical literature.
- It is worth recalling that the incidence of Back Mice is 16% in the general population, (Curtis P, 1993). The interest in BM is increasing, for example, a musculoskeletal sonographic demonstration of BM has been published recently (Bicket et al, 2016; Tiegs-Heiden et al, 2017).
The authors put forward a case report about a patient with LBP and BM, where the diagnosis was done clinically and by ultrasound. Subsequently, back mice was demonstrated by magnetic resonance imaging (MRI) in three different sequences.
Jansen and Degn’s Case report: Clinical Examination
The findings reported by Jensen and Degn about a patient of 67-year-old male are described below, who was referred to a surgical evaluation of two painful masses in the lumbar region. These masses had been present for around 5 months.
- The patient described increasing pain and lacking effect of analgesics, the pain was particularly located on the right lumbar mass and was without radiation.
- The pain was not aggravated by any specific position or activity, and the patient was pain-free when the masses were left untouched. By contrast, he experienced increasingly pain and sensitivity with even gentle touches.
- The patient had no neurological deficits nor myalgia and no vascular impairments in the lower extremities. Routine rheumatological blood samples were inconspicuous.
- Figure 1 illustrates the clinical examination reported by the authors, where a mobile mass on both sides of the midline on the level of the fifth lumbar vertebral was found.
Figure 1: Photo of a 67-year-old patient with lower back pain related to Back Mice (BM), red circular markings surround the patient’s BM located in the sacroiliac area.
Case report: Sonographic evaluation
- The outcomes of the sonographic evaluation are shown in Figure 2, where the authors found two 2×1.5×0.5 cm masses located between the superficial and deep fascial planes near the level of the posterior iliac spine.
Figure 2: Longitudinal sonographic image of the right-sided subfascial fat herniation (Back Mice) in a 67-year-old male, Star = herniated fat, Arrows = superficial and deep fascia, (Jensen and Degn, 2019).
Case report: MRI outcomes
- A magnetic resonance imaging (MRI) was performed in the 67-year-old male, Figure 3 shows the findings and a summary is presented below:
- A: Coronal T1-sequence with capsule surrounding the BM particularly on the right side.
- B: Sagital T1 fast spin-echo (FSE) sequence showing corresponding fat lobuli.
- C: Axiale short tau inversion recovery (STIR) sequence showing inflammation in the BM especially on the right side.
- Figure 3: Magnetic resonance imaging (MRI) of the lumbar region in different sequences, a capsule containing fish oil was placed on the skin on top of both back mices, (Jensen and Degn, 2019).
Case report: Treatment
Jensen and Degn explain that the patient was treated with local anesthetic and corticosteroids (2 ml Betamethasone and 3 ml Lidocaine) injected directly into both back mice. Total pain relieved was instantly obtained and the patient was pain-free for 3 weeks, the injection has been repeated 2 times with a similar effect.
Notes about the discussion by Jensen and Degn
- The authors state that the Back Mice is caused by herniation of subfascial fat through a defect in the thoracolumbar fascia.
- They also argue when the fatty tissue is pedunculated the tissue is freely moveable and therefore the fat might be strangulated within the fascia. A local pressure on nerves and vessels in the fat will then cause pain.
- According to (Stockman R, 1904), Back Mice has since discovery in 1904 been considered a clinical diagnosis. The examination will uncover palpable, freely moveable fatty tissue nodules commonly in the sacroiliac region, (Hoy D et al., 2010). Pressure placed directly on these lessons will reproduce the patient’s sensation of pain in the lower back, (Swezey RL, 1991).
- Jensen and Degn suggest a primary treatment for BM with local anesthetic and corticosteroids. A second treatment is the surgical removal of the nodules, but this approach has not been tested thoroughly in recent times.
Jensen and Degn reported the following conclusions:
- The authors explain that low back pain (LBP) is a symptom that accompanies several diseases. Diagnoses of a specific pain generator contribute to targeted therapy which is rewarding for both the physician and the patient.
- They argue that a prerequisite for the correct diagnosis of Back Mice (BM) is knowledge of differential diagnoses that may cause LBP and which test can be used as a diagnostic tool.
- Their case report is relevant because it is the first case demonstrating the visualization of Back Mice using Magnetic Resonance Imaging (MRI) with STIR and FSE. They recognize MRI as a potential tool in BM diagnostic.
- They highlight that the diagnosis of BM is typically clinical, and an ultrasound investigation might help the clinician. They suggest that MRI can be used for BM diagnostic as a supplement in uncertain BM cases.
- However, routinely use of MRI is not recommended as degenerative changes are commonly presented and increases with age irrespective of the presence of LBP.
- Curtis P (1993) In search of the “back mouse”. J Fram Pr 36:657-659.
- Bicket MC, Simmons C, Zheng Y (2016) 2016. Back mice. Pain Physician 19:181-188
- Tiegs-Heiden CA, Murthy NS, Glzebrook KN, Skinner JA (2018) Subfascial fat herniation: sonographic features of back mice. Skeletal Radiol 47: 137-140.
- Stockman R (1904) The causes and treatment of chronic rheumatism. Br Med J 1:477-479.
- Hoy D, Brooks P, Blyth F, Buchbinder R (2010) The Epidemiology of low back pain. Best Pract Res Clin Rheumatol 24:769-781.
- Swezey RL (1991) Non-fibrositic lumbar subcutaneous nodules: prevalence and clinical significance. Br J Rheumatol 30: 376-378.
Published by Marta Cañis Parera in February 2020 (with the collaboration of Mauricio Valarezo)