For the neurologist who deals with MS, the EDSS scale is as commonplace as the trowel for the mason. However, this carries the risk that as a neurologist, one assumes that the EDSS scale is also self-evident for the patient. After talks I recently had, it became clear to me that this is not at all the case. Therefore, I have decided to write a few lines about this rating scale.The principle of the EDSS is that the nervous system is divided into 7 different functional systems. This distinguishes between the visual system (seeing), the motor system (strength and mobility), the brainstem function (e.g., eye mobility), coordination (balance), the sensitive system (sensitivity to touch and pain), bladder function, and cognition (brain performance). Furthermore, the patient’s maximum walking distance is recorded, which is also of great importance for the calculation of the EDSS value.
Each functional system is examined individually and rated with a numerical value. I would like to illustrate this using the examination of the motor system: zero points are given if the motor function is normal, i.e., in the examination, the strength at the extremities is symmetrical, the reflexes are normal and can be triggered symmetrically, hopping on one leg can be done at least 10 times smoothly, and the tone of the muscles is normal. One point is awarded if an abnormal finding is found that is not relevant to the patient, e.g., a reflex difference in the lower extremity. Two points are given for a slight restriction, i.e., hopping on one leg is less smooth and is not maintained 10 times. Three points would be given for a mild paralysis of the lower extremity (paraparesis) or a half-side paralysis (hemiparesis), four points if the paraparesis or the hemiparesis has a clearly disabling extent. Five points are calculated for complete paralysis of the legs (paraplegia) or a complete half-side paralysis (hemiplegia). Finally, six points are awarded for complete paralysis of all 4 limbs (tetraplegia). Thus, each functional system is rated with a score of 0 – 5 or 6. There are clear rules for the rating – anyone who wants can look it up precisely on the homepage of neurostatus.net.
When each system has been rated with a point value, the EDSS is formed from the constellation of point values – EDSS stands for “expanded disability status scale,” or in German “erweiterte Behinderungsskala,” where the expansion consists of combining the point values according to certain rules into an EDSS value. This methodology was introduced in 1983 by John Kurzke and is still the most widely used rating system for MS disease, even though it admittedly has many weaknesses.
The EDSS scale ranges from 0 – 10 points and increases from EDSS 1.0 in 0.5 point increments. Here are a few examples of how an EDSS value is calculated:
EDSS 1.0 means that there is no disability, but a disorder was found in one functional system that was rated with grade 1. EDSS 3.0, on the other hand, means that one has a moderate disability in one functional system (i.e., rating with grade 3) or alternatively a mild disability in three or 4 functional systems (grade 1- 2). For the EDSS values from 4.0, the length of the maximum walking distance also plays a role and is included in the rating – and even dominates the rating of the functional system. Thus, EDSS 6.0 means that the affected person can still walk 100 m with a unilateral walking aid (without a break), the functional scores are usually grade > 3, but are of secondary importance in this range of the EDSS. For the EDSS values above 7.0, a functional rating is in the foreground. EDSS 8.0, for example, means that the affected person is primarily confined to bed or wheelchair, but still has a largely unaffected arm function.
This description already shows the weaknesses of the EDSS scale – it is strongly defined by the motor function. Performance changes (fatigue) or cognitive disorders hardly go into the rating. Moreover, it is an ordinal scale, and the transitions between the individual values have quite different significances for the patient – so a transition from EDSS 1.0 to 2.0 is probably imperceptible for the patient and only of interest to the doctor, while the transition from EDSS 3.0 to 4.0 is accompanied by a significant restriction of mobility. Accordingly, the scale also does not have a high discriminative power. And to form averages, as is done in many studies, is actually nonsense.
On the other hand, the scale is widespread worldwide and has a high acceptance. When doctors on different continents talk to each other, for example, the EDSS value provides a good description of the condition of an MS patient across borders. Furthermore, the EDSS has been serving for decades as a measurement parameter in clinical studies – our entire guidelines and therapy algorithms are based on it.
Nevertheless, because of the aforementioned disadvantages, we actually need better rating systems. Some things have been set in motion in recent years, but so far it has not been possible to replace the EDSS. Therefore, the scale will certainly accompany us for many more years, and its knowledge is therefore still important.
