Lisa Costelloe, Department of Neurology, Beaumont Hospital, Dublin, Ireland

Whilst the majority of people with MS initially have the relapsing-remitting variant of the disease (see page 7) and go on to enter the secondary progressive phase (see page 13), a small proportion will have a milderthan- usual course, so-called benign MS, and another minority will have a more aggressive course from the outset.

Benign MS
Some people live with MS for many years without accumulating disability. This group has so-called benign MS, the reported frequency of which varies between 5% and 40% in studies. It is the mildest form of MS that is clinically apparent. People with benign MS have a minimal amount of physical disability after ten years or more of the disease.

Clinical predictors of a benign course vary but several studies have found that female gender, younger age at onset, and less disability early in the disease course, are more predictive of a benign course in the long term. Abnormalities on conventional MRI do not necessarily correlate with disability and people with benign MS may have a large number of lesions on MRI despite relatively minimal clinical features.

Early identification of benign MS would be important in deciding who should or should not take lifelong disease-modifying treatments. However, benign MS cannot be diagnosed at the onset of the disease but only becomes clear over time. Moreover, long-term follow-up has found that many people with benign MS do go on to develop progressive disease, and therefore labelling someone as having benign MS too early in the disease course may be misleading.

Malignant MS
This MS variant, previously referred to as Marburg’s MS, was first described by Otto Marburg in 1906 and it is, thankfully, very rare. This is an aggressive form of MS that is characterised by rapid accumulation of disability and death within a few months to a year of the onset of symptoms. This type of MS is poorly responsive to standard MS treatment, although there are some reports of a response to mitoxantrone in individual cases.

Devic’s disease, also known as Devic’s syndrome or neuromyelitis optica (NMO), is a rare disorder that resembles MS in several ways.

As in MS, the body’s immune system attacks the myelin surrounding nerve cells. Symptoms are similar to those seen in MS, although mainly associated with transverse myelitis and optic neuritis. Currently, there is no cure for Devic’s disease, but symptoms can be treated and corticosteroids can be given.