There are, of course, many different causes of myelopathy, several of which are more common than syringomyelia, but syringomyelia should always be considered in the differential diagnosis of any case of spinal cord disease (Honan and Williams 1993). The hallmarks of myelopathy associated with syringomyelia include muscle weakness and atrophy at the level of maximal syrinx formation, very often localised to the hands and forearms, in association with long tract signs involving mostly the lower extremities. Pain seen with syringomyelia tends to be diffuse and neuropathic in character. Cervical spondylotic myelopathy is by far the more common cause of myelopathy and is often associated with pain and motor findings in nerve root distribution. Long tract signs may be more prominent than with syringomyelia, and upper extremity reflexes, often absent in syringomyelia, are often preserved and sometimes hyperactive in cervical spondylotic myelopathy. The latter condition results from acquired narrowing of the cervical spinal canal, due to osteophyte formation, and is therefore more likely to be seen in an older patient group than is syringomyelia. Radicular pain is more acute, may be positionally related and may respond to cervical traction.

Other forms of myelopathy, including those due to so-called neurodegenerative disorders, including motor neuron disease and various viral disorders (e.g. HIV and tropical spastic paraparesis), also must be considered. Magnetic resonance imaging is, of course, now fundamental to establishing a correct diagnosis.

The increasing use of magnetic resonance imaging (MRI) studies, in people who have suffered relatively minor injuries and accidents, has led to an increase in the number of patients who have been diagnosed with “small syringomyelia cavities”, which are actually moderately distended or simply persisting central canals , of the type commonly referred to as hydromyelic cavities (Holly and Batzdorf 2002). Sometimes one encounters patients with more sizeable, relatively distended cavities which may not be in any way symptomatic and which may not generate any physical signs. It has been suggested that such cavities may represent a form of “compensated hydromyelia”, in a manner analogous to the so-called compensated hydrocephalus. On occasion, however, a traumatic origin of such a cavity may be missed, when a history of an injury many years previously is overlooked.

Symptoms of Chiari malformation and syringomyelia often first develop in adult patients in their 20s or 30s, yet we are dealing with bony and other anatomical features which were, presumably, fully developed at puberty. One possible explanation is that the exertional manoeuvres, which are part of daily living, cause very gradual incremental descent of the tonsils. It is also recognised that trauma, such as a sudden jarring of the head, or prolonged bout of severe coughing may bring about a sudden onset of symptoms in a previously asymptomatic patient. Presumably this is also the result of an increase in tonsillar descent. With syringomyelia similarly, symptoms normally tend to progress gradually, but there are descriptions of sudden symptom development, such as in spinal injury patients following prolonged severe coughing spells (Barnett and Jousse 1973; Foster 1991). Sudden death is extremely rare in patients with Chiari malformation (Friede and Roessmann 1976; Williams 1981), and in most patients the disease progresses either slowly or intermittently. Emergency surgical intervention is rarely, if ever, indicated in these disorders.

When syringomyelia or a Chiari malformation is diagnosed as an incidental finding, there is a potential opportunity for the natural history of the condition to be followed, to determine the rate of progression of the disease in such cases. Unfortunately few such studies have been carried out. The natural history of syringomyelia is discussed further in Chap. 2.

Reviews of cohorts of patients with Chiari malformation, with or without syringomyelia, have provided extensive lists of presenting symptoms, some of which are non-specific (Mueller and Oró 2004). Wide availability of such lists on the Internet, for patients to view, has made it increasingly difficult for clinicians to obtain an uncontaminated history from many patients. As with many other chronic disorders, symptoms of anxiety, memory impairment, depression and sleep problems are encountered not uncommonly in patients with syringomyelia and Chiari malformation. The clinician must weigh all such symptoms with respect to their specificity and particularly as regards the likelihood of the specific symptom being helped by any surgical intervention.