USMLE – Syringomyelia
In this condition a fluid-filled cavity or cavities develops near the center of the spinal cord. The expanding cavity disrupts second-order spinothalamic neurons, may extend laterally to damage the anterior horn cells and may compress the long fiber tracts.
Many patients have some obstruction to the flow of CSF at the foramen magnum. In some this is associated with congenital herniation of the cerebellar tonsils (Chiari type I malformation), and in others with basal arachnoiditis. It is assumed that the disturbed CSF dynamics cause the development of the syrinx but the mechanism is not clear. Rarely, a syrinx develops following spinal cord trauma. Similar cavities may appear in the medulla, producing brain-stem dysfunction (syringobulbia).
Patients usually present in the third or fourth decade and symptoms are of insidious onset and slowly progressive. Pain in the neck or shoulder is common and patients may seek advice because of sensory loss in the upper limbs. The most characteristic physical sign is dissociated sensory loss (impaired pain and temperature sensation with preservation of dorsal column modalities), which has an upper and lower level in a mantle or hemicape distribution. Loss of protective sensory function leads to trophic lesions such as painless burns or ulcers on the hands, and sometimes painless, deranged joints (Charcot joints) in the upper limbs. Wasting of the small hand muscles is a common early feature and loss of one or more reflexes in the arm is usual. Upper motor neuron signs develop in the legs as the condition progresses. Kyphoscoliosis, pes cavus and spina bifida are common associations. Syringobulbia leads to dysarthria, palatal palsy, Homer’s syndrome, nystagmus and sensory loss on the face.
Plain radiographs may demonstrate congenital anomalies around the foramen magnum or expansion of the cervical canal. The most sensitive and least invasive investigation is MRI.
Surgical decompression of the foramen magnum or the syrinx itself may arrest progression of the neurological deficit and often alleviates pain. The results of surgery are however, often disappointing and in some patients the condition continues to progress slowly over long periods.