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A woman with painless burns

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Q1: What is the likely diagnosis?

Syringomyelia.

Q2: What is the differential diagnosis?

Cervical spondylosis, multiple sclerosis, and motor neurone disease (see discussion below).

Q3: What relevant investigations would you request?

Routine blood analysis including erythrocyte sedimentation rate, thyroid function tests, and B12; lateral cervical spine radiography and magnetic resonance imaging (MRI) of cervical spine.

This woman's MRI scans (see figs 1 and 2) revealed a dilated syrinx extending from C2–T3 with characteristic septation in the lower cervical region. There was no evidence of the Arnold-Chiari malformation or a cord neoplasm (see discussion below).

Discussion

Syringomyelia is a rare, chronic, progressive disorder in which tubular cavities form at or close to the central canal of the cervical spinal cord. It typically presents in young adults with a mean age of onset of 30 years.

The condition rarely occurs in isolation. Over two thirds of cases are associated with the Arnold-Chiari malformation in which the cerebellar tonsils herniate through the foramen magnum of the skull. In addition, a syrinx may develop within or in close proximity to an intramedullary tumour, generally a glioma1. Also, cavities in the cord may also develop as a late consequence of cord trauma.

Symptoms depend primarily on the location of the syrinx, but the latter is most commonly located in the lower cervical region. As the syrinx enlarges, it compresses the following structures in the cord:

  • Decussating spinothalamic fibres—results in loss of pain and temperature in a “cape” distribution (with preservation of light touch/vibration sense, that is, dissociated sensory loss) as well as pain radiating from the shoulders down dermatomes which is typically exacerbated by coughing/sneezing; the subsequent impairment of pain sense results in Charot (neuropathic) joints evolving typically at the elbow or wrist.

  • Anterior horn cells—results in wasting and weakness of the small muscles in the hand, spreading proximally.

  • Decussating corticospinal tract fibres—results in a spastic paraparesis in the lower limbs with extensor plantar responses.

  • Cervical sympathetics—results in a Horner's syndrome and/or disturbances in sweating (hyper or hypohydrosis).

As the syrinx is usually asymmetrically placed, manifestations in the arms and hands tend to be similarly asymmetric. It is worth noting that sphincter function is typically preserved until very late on in the disease process.

The syrinx may ascend into the medulla. So called syringobulbia is evidenced by dysphagia, palatal weakness, nystagmus, asymmetric weakness of the tongue with atrophy, and dissociated sensory loss in the distribution of the trigeminal nerve.

Important differential diagnoses to be excluded include cervical spondylosis, multiple sclerosis, and motor neurone disease; they may all cause a spastic paraparesis with upper limb neurological signs, but there are important differences. Cervical spondylosis is common, but not within young adult populations. It may be impossible to exclude on neurological examination and of course may actually coexist with a syrinx! Important clues are reduced range of neck movements and neck pain. Multiple sclerosis does present in this age group, but there will be no dissemination in time and location of the central nervous system symptoms/signs and early wasting of the hand muscles is not a feature of multiple sclerosis. Motor neurone disease may cause weakness, wasting, and loss of reflexes in the upper limb but patients tend to present in middle age, there are no sensory signs, and early fasciculations of the upper limb muscles is an early sign.

Another differential to exclude is that of an intrinsic spinal cord neoplasm. As mentioned above, this may coexist with a syrinx. From the discussion below it is noted that the tumour may actually be involved in the pathogenesis of syringomyelia. Thus gadolinium enhanced MRI is an essential investigation in the work-up of such patients in order to exclude an intrinsic cord neoplasm.

The pathogenesis of syringomyelia is uncertain, but various theories exist.2,3 The hydrodynamic theory depends on the obstruction of the normal outlets of the fourth ventricle by developmental or other anatomical anomalies. By this theory, it is the abnormal cerebrospinal fluid (CSF) pulsations that lead to the enlargement of the cavity. Alternatively, it has been proposed that the Arnold-Chiari malformation is an acquired anomaly secondary to excessive moulding of the head during difficult, usually high forceps, deliveries. The subsequent deformity could dissociate pressures between cranial and CSF spinal pressures, leading to syrinx formation. Numerous other theories include cystic degeneration of an intramedullary glioma or after resorption of an intramedullary haematoma after cord trauma.

MRI is the diagnostic test of choice. Cystic enlargement of the cord generally extends over several segments with signal intensity similar to that of CSF. Cyst margins are typically irregular with folds and septations. If a syrinx is identified, one must specifically look for craniovertebral junction anomalies and intramedullary tumours (with gadolinium enhancement).

Management of these patients is controversial and varies from a “wait and see” policy to one of aggressive neurosurgery.4 On a background of slowly progressive minimal disability, the associated morbidity of surgery and a lack of unequivocal benefit from most surgical series, many neurologists advocate a conservative approach. On the other hand, many recommend neurosurgical treatment, especially in the context of severe/rapidly progressive symptoms, cord neoplasms, or an Arnold-Chiari malformation. In tumour associated syringomyelia, excision of the mass nearly always results in resolution of the syrinx. In post-cord trauma patients, simple drainage by percutaneous needle aspiration or open syringotomy provide temporary relief at best, as the cavity will re-expand on spontaneous closure of the syringotomy. Prolonged successful drainage necessitates placement of a silastic tube connecting the syrinx to either the pleural or pericardial space. In Arnold-Chiari associated syringomyelia, ventriculoperitoneal shunting is normally performed if there is significant hydrocephalus present. If no hydrocephalus is present, or if shunting fails to relieve symptoms, posterior fossa decompression usually shrinks or even completely resolves the syrinx.

Final diagnosis

Syringomyelia.

References

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