Low Back Pain Revealing an Inborn Metabolic Disease: A Case Report
2Department of Rheumatology, University Hospital of Tours, France
3Biochemistry laboratory, University Hospital of Tours, France
4Biochemistry and Molecular Biology Department, University Hospitalof Lyon, France
Background. Acute low back pain is mostly related to osteoarticular spinal diseases and occasionally to muscular diseases. We present a case of low back pain revealing a metabolic myopathy.
Case report. A 17-year-old man with a history of sensorineural hearing loss and Helicobacter pylori gastritis was admitted for acute disabling low back pain. Clinical examination showed stiffness and an edematous aspect of the lumbar paravertebral muscles. Walking was impossible because of the intensity of lumbar pain. Biochemical tests showed plasma CRP 202 mg/L and CKs 66,000 IU/L. The spinal MRI showed features of necrotising myofasciitis involving the erector spinae muscles of the lumbar iliocostalis, longissimus of the thorax, transverse spinous and square muscles of the lumbar spine, bilaterally extended opposite L1-S3. The muscle biopsy showed signs of complete muscle necrosis. The autoimmune workup, including dot-myositis, was negative. After analgesic treatment with morphine and rest, the pain regressed and the CKs decreased to 1948 IU/L. The subsequent evolution was clinically favorable and the MRI showed clear signs of muscle improvement. CKs remained high over time between 1116 and 1752 IU/L. Investigation showed that the patient had had exercise intolerance from childhood, with a clear limitation of sports activities. The grip test revealed an absence of elevation of lactacidaemia: 0.70 mmol/L before exercise and maximum at 1.18 mmol/L post-exercise, indicating McArdle’s disease. This diagnosis was confirmed by molecular analysis of the PYGM gene showing a compound heterozygosity c.1963GA/c.2178-1GA (2 pathogenic variants).
Discussion/conclusion. McArdle’s disease is a muscular glycogen storage disease (GSD 5) usually revealed by muscular intolerance to effort, including a "second wind" phenomenon that our patient did not clearly describe. Muscle involvement usually predominates in the lower limbs. The involvement of the paravertebral muscles of GSD 5 is not well known because it is rarely in the foreground of the clinical picture of GSD5, as in our case. Nevertheless, deficits in the paraspinal muscles have been described and recent MRI studies have shown that axial muscle damage is underestimated. Clinical involvement of the paraspinal muscles is rare in GSD 5. A revelation of the disease by acute rhabdomyolysis of the paraspinal muscles has not been described to date.
.png)