Achondroplasia is an autosomal dominant inherited mutation in the fibroblast growth factor receptor-3 gene on the short arm of chromosome 4. It is the most common form of human skeletal dysplasia, with frequency of 1/15,000–1/40,000 live births. We report an illustrative case of spinal stenosis combined with thoracolumbar kyphosis (TLK) deformity and ossification of the ligamentum flavum (OLF) in a 39-year-old man with known achondroplasia.
The patient has developed paresthesia in both legs for 6 months, and visited emergency department because of left leg weakness. Motor grades of both lower extremities were initially Poor and paresthesia was observed below L2 dermatome. The whole-spine x-ray showed TLK with a Cobb angle of 34˚ (Figure 1). CT scan and T2-weighted MRI revealed pedicle shortenings in multilevel, resulting spinal canal stenosis and cord compression with syrinx, and scalloping of posterior vertebral bodies of lumbar spines, which are relevant to achondroplasia (Figure 2). Degenerative disc diseases of lumbar spines with severe central spinal stenosis at L1-S1 were also found. Compression fractures of L1 and L2 vertebrae were shown, with retropulsion of L2 on L3. Additionally, OLF with cord compression and myelopathy were found at D9-D11 level in whole-spine CT and MRI (Figure 2).
The patient underwent surgery with posterior instrumentation and decompressive total laminectomy at L1-S1, and hemi-laminectomy at D9-D11. He was transferred to department of rehabilitation medicine at POD#14. After 2 weeks of rehabilitation therapy, muscle power improved from Poor to Fair grade, and he was able to ambulate with walker under supervision.
The factors associated with progression of thoracolumbar kyphosis and spinal stenosis have been thought to be associated with biomechanical factors such as generalized hypotonia, a large head, lax ligaments, hip flexion contracture with unusual vertical load on the anterior column of the spine. Progression to a fixed kyphotic deformity is known to occur in 15–30% of adults. Neurological symptoms associated with lumbar spinal stenosis are present in a significant proportion of patients with achondroplasia, and about one third will require surgery. Yet, there is no consensus that how severe TLK may have risk for cord compression, and in which patient group has risk for development of OLF in achondroplasia.
In the early course of the disease, a careful observation with conservative therapy including proper brace, hip stretching, lumbar spine stabilization, restriction of slump sitting to delay thoracolumbar kyphosis deformity may be helpful. Nevertheless, whenever fixed deformity with neurologic manifestation is developed, timely surgery should be needed. |
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The whole-spine sagittal x-ray of the patient, showing upper lumbar kyphosis with Cobb’s angle of 34 degree.
The CT scan shows multilevel spinal stenosis, compression fractures, and ossification of the ligamentum flavum (OLF) at lower thoracic spine level (A, B). The MRI shows thoracic cord compression due to OLF (arrow), syrinx formation at upper lumbar spinal cord level (dashed arrow), and compression of the conus medullaris due to L2 vertebra retropulsion (bold arrow).
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