The patient was generally fit and well, with no history of neurological symptoms. Though he had recently seen an osteopath for problems with his right shoulder, he otherwise had no past medical history and was taking no regular medication. A non-smoker, he consumed little in the way of alcohol and had an unremarkable family history.

The cardiovascular examination was normal. Neurological examination was normal, apart from slightly brisk left-arm reflexes.

All variants share certain common features.² As in the case presented here, the symptoms are often brief, persisting for a few seconds but recurring many times each day, leaving the patient normal during the period between attacks. Although the individual episodes are brief, the time scale of a cluster of paroxysmal symptoms, typically days to months followed by remission, is similar to that of a relapse of multiple sclerosis. Symptoms are often stereotyped, may be individual to the patient and are frequently triggered by sensory stimuli, over breathing or, as in this case, by movement. With their sudden onset, they are easily attributed to epilepsy, transient ischaemic attacks, anxiety or labelled as functional and may even bewilder competent neurologists. Though probably underrecognised, they are most common early in the course of multiple sclerosis,³ with 8.6% of patients experiencing paroxysmal symptoms at some stage¹ and some experiencing more than one form over time, suggesting demyelination in different areas. They are particularly common in patients from Japan and Taiwan.⁴

The most well-recognised types of paroxysmal symptoms are given here in the order of likely prevalence on the basis of case series (eg, reference ⁵). There is general agreement that 2% of people with trigeminal neuralgia have multiple sclerosis and 1% of people with multiple sclerosis will have trigeminal neuralgia.⁶ The pain is similar to that experienced with the idiopathic form, only more often bilateral.⁷ Frequently overlooked as dizziness, cerebellar ataxia frequently occurs with dysarthria. Tonic spasms can affect the face or limbs and may manifest as a transient disturbance in handwriting. Sensory symptoms, including numbness and pain typically occurring in the limbs or face, can be difficult to diagnose owing to their transient nature. Itching is recognised and is often intense. Akinesia, with paroxysmal loss of function in one or more limbs, may also be encountered. Paroxysmal involuntary movements, however, are usually the result of comorbidity rather than demyelination.⁸

The postulated mechanism provides a rationale for the treatment of these frequently troublesome symptoms. After a period of reduced excitability following demyelination, some axons become hyperexcitable. These then spontaneously discharge and may activate groups of neighbouring neurons via ephaptic transmission.⁹ Demyelinated sensory neurons are probably more prone to hyperexcitability owing to the greater expression of sodium channels.¹⁰ On this basis, membrane-stabilising drugs are prescribed in low dosages, and almost all patients respond rapidly.²

It is important that paroxysmal demyelinating events are not missed to facilitate a timely diagnosis, initiate appropriate treatment and identify relapses. In this case, with the history of leg numbness occurring a year prior to the paroxysmal symptoms and the positive MRI findings a diagnosis of probable multiple sclerosis was made.