Age / Sex : 61 / M

Chief complaint: back pain, both upper and lower extremity weakness for 4 years

Muscular dystrophy

Discussion

Findings:

Selective fatty replacement is seen at erector spinae muscle symmetrically. The psoas, and multifidus muscles are relatively spared.

Differential Diagnosis:

1)     Normal fatty infiltration in elderly person

2)     Fatty infiltration of paraspinal muscle related to chronic low back pain

3)     Degenerative kyphosis

4)     Postoperative fatty infiltration of muscle

5)     Poliomyelitis

Diagnosis:  Muscular dystrophy

Discussion:

l  Muscular dystrophy: symmetric fatty replacement of erector spinae muscle is reported with relatively sparing of psoas muscle, and quadratus lumborum muscle (1). Total fatty replacement of the erector spinae muscle is reported in long standing case (1).

l  Differential diagnosis

1.     Advanced age: fatty replacement and atrophy change of paraspinal muscles is a normal age-progressive phenomenum, most prominent in females. It progressed down the spine, being most advanced in the lumbosacral region. However the total replacement of muscle by fat just as in this case is very unusual (1).

2.     Chronic low back pain:

Mengiardi et al (2) compared fat content of multifidus muscle and longissimus muscle between patients with chronic low back pain and normal volunteer matched with age, sex and body mass index. According to their study, patient group with chronic low back pain showed significantly higher fat content in the mutifidus muscle than normal volunteer group. However, the fat content of longissimus muscle did not show significant differences between two groups. Recent studies also supported the multifidus muscle is important muscle for lumbar instability (3)

3.     Degenerative lumbar kyphosis: According to Kang et al (4), patient with lumbar degenerative kyphosis had a higher proportion of fat deposits in both multifidus and erector spinae muscle.

4.     Postoperative condition: Fatty infiltration and atrophic change of paraspinal muscle after back surgery are usually developed around spinous process and transverse process due to denervation, ischemic necrosis of muscle related to muscle dissection ( 5)

5.     Poliomyelitis: Unilateral fatty atrophy and fatty replacement of paraspinal muscle were reported in patients with poliomyelitis. Some cases shows unilateral “ total washed out” of erector spinae, quadratus lumborum, and multifidus muscle in patient with long standing poliomyelitis (1)

References:

1. Hadar H, Gadoth N, Heifetz M. Fatty replacement of lower paraspinal muscles:normal and neuromuscular disorders. AJR Am J Roentgenol. 1983 Nov;141(5):895-8.

2. Mengiardi B, Schmid MR, Boos N, Pfirrmann CW, Brunner F, Elfering A, Hodler J. Fat content of lumbar paraspinal muscles in patients with chronic low back pain and in asymptomatic volunteers: quantification with MR spectroscopy. Radiology. 2006 Sep;240(3):786-92

3. Panjabi M. The stabilizing system of the spine I Function, dysfunction, adaptation, and enhancement, J spinal Disord 1992:5:383-9

4. Kang CH, Shin MJ, Kim SM, Lee SH, Lee CS. MRI of paraspinal muscles in lumbar degenerative kyphosis patients and control patients with chronic low back pain.Clin Radiol. 2007 May;62(5):479-86. Epub 2007 Feb 22. PubMed PMID: 17398274.

5. Hartwig T, Streitparth F, Gross C, Müller M, Perka C, Putzier M, Strube P. Digital 3-dimensional analysis of the paravertebral lumbar muscles after circumferential single-level fusion. J Spinal Disord Tech. 2011 Oct;24(7):451-4.


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