NORMAS GENERALES

The study of the natural history of MS is made particularly difficult by its long duration and markedly varied clinical course. Several differing approaches have been used.

1.1.7.1 Relapse rate: Relapses occur more commonly in young patients and decrease

in frequency with disease duration regardless of the disease course [Lhermitte et at.

1973]. On average a patient with relapsing-remitting MS suffers approximately one relapse per year [IFNB MSSG 1993, Johnson et al. 1995, Jacobs et al. 1996, PRISMS

1998], although some patients may suffer many more and many far less.

1.1.7.2 Disability: Disability results from either incomplete resolution of relapses in

the relapsing-remitting stage or due to progressive deterioration in primary or secondary progressive MS patients. Most studies have found that only 50% of MS patients are independent and able to walk after 15 years [Confavreux et al. 1980,

Weinshenker et al. 1989, Runmarker & Andersen 1993]. For research purposes,

disability in MS is measured using disability scales, such as the expanded disability status scale (EDSS) described by Kurtzke (Table 1.3) [Kurtzke 1983]. The EDSS is based on ambulation and scores from different functional systems, i.e. pyramidal, cerebellar, brainstem, vegetative, visual, sensory, cerebral and other. It is heavily weighted towards walking ability in the higher scores and is not a linear measurement.

Table 1.3 Kurtzke’s Expanded Disability Status Scale (EDSS)

0 = Normal neurological examination (all FS normal, mild cerebral signs acceptable) 1.0 = No disability, minimal signs in one FS

1. 5= No disability, minimal signs in more than one FS 2.0 = Minimal disability in one FS

2.5 = Minimal disability in two FS

3.0 = Moderate disability in one or mild disability in up to four FS though fully ambulatory 3.5 = Fully ambulatory but with a moderate disability in one FS and mild disability in one

or two others; or moderate disability in two FS; or mild disability in five FS 4.0 = Fully ambulatory without aid; self-sufficient; up and about some 12 hours a day

despite relatively severe disability in one FS or combinations of exceeding the limits of the previous step. Able to walk without aid or rest for 500m.

4.5 = Fully ambulatory without aid; up and about much of the day; may otherwise have some limitation of full activity or require minimal assistance. Able to walk without aid or rest for 300m

5.0 = Ambulatory without aid or rest for 200m; disability severe enough to impair full daily activities.

5.5 = Ambulatory without aid or rest for 100m; disability severe enough to preclude full daily activities.

6.0 = Intermittent or unilateral constant assistance required to walk 100m 6.5 = Constant bilateral assistance to walk 20m without rest

7.0 = Unable to walk 5m even with aid. Essentially restricted to a wheelchair. Transfers alone.

7.5 = Unable to walk more than a few steps. May need aid with transfers

8.0 = Restricted to bed or chair or perambulated in wheelchair. Generally has effective use of arms. Out of bed for much of day

8.5 = Essentially restricted to bed for much of the day. Retains some self-care functions 9.0 = Helpless bed patient; can communicate and eat

9.5 = Totally helpless, unable to communicate effectively or eat /swallow 10.0 = Death due to MS

but it enables comparison of disabilities between groups o f patients with some degree o f consistency. Several longitudinal studies of disability in MS have now been performed [Confavreux et al. 1980, Weinshenker et a l 1989, Phadke 1990,

Runmarker & Andersen 1993]. Factors that have been found to indicate a better or worse prognosis are summarised in Table 1.4.

Table 1.4 Early predictors of disability in MS

Better

Female sex

Onset: remitting, sensory / optic neuritis Complete recovery from relapse

Long inter-attack interval Low relapse frequency Long time to EDSS 3 Younger age

Mono symptomatic presentation

Worse

Male sex

Onset: progressive, motor

Incomplete recovery from relapse Short inter-attack interval

High relapse frequency Short time to EDSS 3 Older age

Polysymptomatic presentation

Several studies have found the disability status at five years to be strongly predictive of future course [Kurtzke et a l 1977b, Weinshenker et a l 1989, Miller et a l 1992a].

The early clinical course also appears, at least in some studies, to be important in determining future disability. A high frequency of relapses in the first two years after the onset o f MS has been associated with increased disability after prolonged follow- up [Weinshenker et a l 1991]. This finding was, however, contrary to those of

Runmarker & Andersen [1993], who described no such association. This difference may be accounted for by the inclusion of patients with progressive disease in the latter study, in whom a rapid increase in disability in the absence o f relapses is the usual course.

Most studies of disabihty in MS have focused on physical problems, but it has become increasingly recognised that cognitive problems also frequently (40 - 60%) occur in MS patients and may be marked [Minden et a/. 1987]. The pattern of

cognitive decline is variable. Often the effect on attention, memory and information processing is greatest, although a lesser effect on language function may mask the severity o f the deficit [Rao et al 1991]. These cognitive deficits may remain static for

many years but do appear to be worse in patients with secondary progressive disease [Ron et al 1991]. Psychiatric problems, particularly depression, may also occur in MS

contributing to overall disability and quality of life and contribute to the increased risk of suicide seen in MS patients [Sadovnick et al. 1991, Stenager et al. 1992]. Euphoria,

an organic personality change with a chronically elevated mood, has previously been over reported in MS and probably only occurs in 10% of patients [Diaz-Olavarrieta et

al. 1999].

1.1.7.3 Temporal course: The time to conversion from relapsing-remitting to

secondary progressive MS is an important prognostic landmark in the development of MS. This usually occurs when the patient has an EDSS o f about 4.0 [Runmarker & Andersen 1993]. Once a progressive course has become established the development of an EDSS of 6.0 usually occurs within 3 - 7 years [Runmarker & Andersen 1993].

with this method of studying natural history of MS is that the diagnosis of secondary progression can only be made retrospectively, after at least six months o f continued deterioration.

1.1.7.4 Survival studies: Studies performed since the introduction of antibiotics have

found a 75 - 85% survival rate in MS patients 25 years after the onset of the disease. MS has little influence on the cause of death until at least 15 years into the illness. Survival studies are an insensitive measure in MS because half o f deaths are not disease related; being caused by conditions that affect the population as a whole, such as vascular disease or malignancy. Death nevertheless may occur due to complications of severe MS, such as pneumonia or urinary tract infection and overall life expectancy is reduced by about five years [Phadke 1987, Sadovnick et al. 1992].

The risk of suicide is increased in MS populations, being several times than o f an age- adjusted general population [Sadovnick et al. 1991, Stenager et al. 1992].