Figure – This T1-weighted MRI scan of the patient's spine shows a syrinx extending from C3 to the conus medullaris and an associated Chiari I malformation.
The MRI of the spine shows a large syrinx extending from the level of the third cervical vertebra to the conus medullaris, leading to a diagnosis of syringomyelia. A Chiari I malformation is also visible (Figure).
Before the laboratory results and MRI were obtained, the differential diagnosis was extensive (Table). Results of the history taking and physical examination—especially the combination of loss of deep tendon reflexes (more of a lower motor neuron problem) and a possible gait disturbance (more of an upper motor neuron problem)—made it difficult to confine the differential to one area of the neurological system. The process of narrowing it was further complicated by the necessity of determining the location of the lesion and assessing gait in a patient with a developmental disability.
Initially, Guillain-Barré syndrome (GBS), acute disseminated encephalomyelitis, and multiple sclerosis seemed the most likely possibilities. Although GBS is usually preceded by a diarrheal illness, the rare variant of GBS called Miller Fisher syndrome typically presents with the classic triad of ataxia, areflexia, and ophthalmoplegia.1 MRI helped to clarify the picture.
Syringomyelia: an overview. Syringomyelia is defined as a fluid-filled cavity within the spinal cord. Its pathogenesis is unclear and controversial. Syringomyelia can either communicate with the central cerebrospinal fluid canal or be localized and noncommunicating. The communicating type is strongly associated (more than 25% of cases) with Chiari I malformations (displacement of the cerebellar tonsils and posterior vermis through the foramen magnum). The noncommunicating type can be associated with spinal neoplasms (such as cystic astrocytomas), trauma, or arachnoiditis.2 Syringomyelia is a classic nontraumatic cause of central cord syndrome.3 Compressive forces from the syrinx have the most damaging effect on the central mass of the cord substance and can affect motor recovery.
Presentation. The presentation of patients with syringomyelia varies with the location and size of the syrinx. A syrinx can be asymptomatic and discovered incidentally on spinal cord imaging. Because of their slow evolution, lesions rarely produce symptoms in childhood. Syringomyelia associated with Chiari I malformations usually presents in young adulthood; the initial symptom is typically a suboccipital headache exacerbated by exertion (eg, coughing) accompanied by diffuse neck pain.4
Interruption of the crossing fibers of the lateral spinothalamic tracts causes loss of pain and temperature sensation at the level of the spinal cord lesion, with preservation of the senses of light touch, vibration, and position. These sensation deficits can lead to the development of fingertip ulcers.
As the cavity expands, involvement of the ventral anterior horn cells can lead to weakness, atrophy, and loss of deep tendon reflexes. Involvement of the posterior dorsal columns can lead to vibration and touch disturbances. Upper motor neuron signs, such as spasticity and hyperreflexia, usually develop in the lower extremities; however, long cavities may produce lower motor neuron signs in all limbs.2,5 Upward extension of the cavity into the lower brain stem, which is known as syringobulbia, can result in dysarthria, nystagmus, and decreased sensation of the face. Patients can also present with progressive scoliosis, torticollis, or neuropathic pain.6
Disease course and treatment. Syringomyelia usually has a chronic, stable, clinical course. Asymptomatic patients are often followed up conservatively with serial imaging studies and neurological examinations.6
In patients with syringomyelia who have progressive scoliosis or progressive motor and/or sensory loss, surgical treatment is appropriate. Emergent surgery (choice A) is usually not warranted. In particular, the absence of syncope, apnea, or a history of aspiration in this child argued against immediate intervention.7 However, waiting 6 months to reevaluate the patient (choice D) would not be appropriate either, since he has had progressive worsening of symptoms.
In children with an associated Chiari malformation, decompression of the foramen magnum and laminectomy of the upper cervical vertebrae relieves the symptoms caused by compression of the tonsils (eg, posterior neck pain, tussive headache, apneic spells). However, diminishment of the symptoms caused by the syrinx itself (eg, weakness, atrophy, loss of deep tendon reflexes) is variable and unpredictable.8 If decompression does not reduce the size of the syrinx, shunting of the cavity may be required; however this is very rare.1
Syringomyelia unaccompanied by a Chiari malformation may require a posterior fossa decompression. However, this only occurs under special circumstances.9
Intravenous corticosteroids (choice C) do not have a role in the treatment of syringomyelia. Corticosteroid treatment might be considered in a patient whose symptoms were associated with a postinfectious reaction, such as acute disseminated encephalomyelitis or transverse myelitis. However, management of syringomyelia is primarily surgical; muscle relaxants and analgesics can be used for symptom control.
Outcome of this case. This patient underwent posterior fossa decompression with duraplasty the next week. Since decompression, his ambulation has improved; however, he still has mild ataxia. He will need long-term physical and occupational therapy to overcome the residual deficits from his syringomyelia.
|Table — Differential diagnosis of weakness and limp in a 4-year-old boy|