Multiple Sclerosis & Diving

By Dr. Sawatzky

I would like to thank the reader who suggested this column. Multiple Sclerosis (MS) is a very interesting and relatively common disease and the implications for diving are applicable to many other medical problems.

Multiple Sclerosis (also known as disseminated sclerosis, focal sclerosis, insular sclerosis) is defined in Stedmans Medical Dictionary (1994) as "the occurrence of patches of sclerosis (plaques) in the brain and spinal cord causing some degree of paralysis, tremor, nystagmus, and disturbances of speech, the various symptoms depending upon the seat of the lesions; it occurs chiefly in early adult life, with characteristic exacerbations and remissions". Now, lets take this definition apart and translate it into common English. It should be noted that knowledge about this disease is continuing to develop. Most of the information in this column is taken from Scientific American Medicine on CD, October 1997 edition (the actual section was written in 1993, each section is updated as required with a new version of the entire reference coming out every three months).

In simple terms, the brain can be thought of as a large number of interconnecting nerve cells supported by a mesh of other types of cells. The nerve cells communicate with each other and with the body through extensions of the cell called axons. The axons can be thought of as biologic wires. Like wires, axons need to be insulated to allow the signals to be transmitted properly. This insulation is provided by a special cell that wraps around the axon and is called myelin. In MS, the myelin is destroyed in patches throughout the brain and spinal cord. Without myelin, the impulses either travel very slowly down the axon or they are completely blocked. These areas of dysfunction cause the signs and symptoms of multiple sclerosis.

Early in the disease process the myelin reforms on some of the axons. In addition, biochemical changes (sodium channel density increases in the demyelinated axon) sometimes allow the axon to start to function again when only a short segment has been demyelinated. This return of function is why the signs and symptoms of MS usually get better after the first attack. With time and continued attacks however, the recovery is less complete and the person develops progressively worse signs and symptoms. This explains the two primary requirements for a diagnosis of MS; involvement of multiple locations in the nervous system and a history of getting worse and then at least partially recovering.

Although the cause of MS is unknown, several interesting epidemiological observations have been made. The disease is 10 to 20 times more common in temperate climates than in the tropics. If a person moves from a temperate area to the tropics before the age of 15, their risk of MS is the same as if they had lived in the tropics all their life. Conversely, if they move from the tropics to a temperate area before the age of 15, their risk of MS is the same as if they'd lived in a temperate area all their life. However, if a person moves after the age of 15 their risk of MS is the same as if they had not moved. The disease is more common in people who live in cities and in more affluent socioeconomic groups. These observations strongly suggest that a virus might be involved in causing the disease.

Multiple Sclerosis appears to becoming more common with an incidence of about six cases for every 100,000 people in the United States. Men who develop MS tend to die earlier than expected but women tend to live a normal life-span.

Genetic factors are also important with several specific HLA tissue types having an increased incidence of MS. In identical twins, if one twin develops MS the second twin has a risk of 30%. In non-identical twins, the second twins risk is only 2-5%. The fact that 70% of identical twins do NOT develop MS supports the importance of environmental factors (viral infection). First degree relatives (parents, brothers, sisters, children) of a person with MS have a 3-5% risk of developing MS. The picture that is emerging from current research is as follows. To develop MS, a person has to have a genetic predisposition, plus a viral infection, plus an abnormal immune response to the viral infection. There is no effective way to prevent or treat MS at this time.

The signs and symptoms of MS partially depend on the areas of the brain and spinal cord that are damaged. It is very rare for the initial signs and symptoms of MS to occur before the age of 15 or after the age of 40 and MS is therefore primarily a disease of young adults. The initial symptoms usually develop over a few days, stay for a few weeks and then go away or at least get much better. Unfortunately, more symptoms tend to develop over time. Clumsiness, stiffness, slowness, weakness, tingling, reduced sensation, and hazy, misty or blurred vision, are examples of symptoms. As the disease progresses, the person develops more and more symptoms and the improvements are less common and less complete. All areas of the brain can be involved. The severity and rapidity of progression are highly variable and it is impossible to predict how the disease will progress in an individual patient.

With this basic understanding of what MS is and how it presents, let's turn our attention to the advisability of a person with MS diving. Several years ago, there was a great deal of interest in using hyperbaric oxygen to treat MS. Several large studies were conducted and it was clearly shown that hyperbaric oxygen had little long term effect, either positive or negative. Therefore, diving and exposure to increased pressure will probably not make MS worse.

Diving is a very physical activity. Patients with MS often have limited stamina and experience has shown that vigorous physical activity is usually not good for them. Therefore, diving that involves a lot of exercise would not be good for an individual with MS. In addition, patients with MS should avoid becoming tired and there is some suggestion that they should avoid becoming cold. Diving, especially in Canada, often involves both of these difficulties.

Another problem is that the person with MS often does not notice trivial symptoms. If they do a dive and after the dive notice that they have a patch of numbness on their leg they have a major problem. Was the patch of numbness there before the dive and they just did not notice it? Is the patch of numbness a result of MS, or is the patch of numbness the result of arterial gas embolism or decompression sickness?

The diving medical literature has very little to say about multiple sclerosis and diving but there are several basic principles that can help us make a decision for the individual patient. The first factor is the person's exercise tolerance. Diving, even a simple shallow dive in the tropics, is much more work than most of us realize (see columns in Aug, Sept, Nov 97). Even if the person has a good exercise tolerance, the advisability of a person with MS engaging in a vigorous physical activity like diving must be considered. A person with MS should avoid becoming cold. Therefore diving in Canada is probably not a good idea for a person with MS.

The most important factor, however, is probably the fact that the signs and symptoms of MS come and go. The development or first observation of a neurological sign or symptom after a dive would demand that the person be evacuated to the nearest hyperbaric chamber and treated. If the person had MS this treatment would not likely harm them but they might experience some short term improvement and enter into a series of treatments, thinking they had a diving injury and were getting better. The inconvenience and expense of a series of treatments can be astronomical. In addition, I can almost guarantee a less than warm reception from the hyperbaric physician at the chamber. Individuals with known neurological signs and symptoms, especially signs and symptoms that change over time, should never dive because of the impossibility of diagnosing arterial gas embolism or decompression sickness in them.

In conclusion, multiple sclerosis is a relatively common disease that primarily affects young adults in temperate climates. The cause is unknown but a genetic predisposition combined with a viral infection and an abnormal immune response to that infection is currently believed to be the most likely explanation. The disease presents as a series of progressively more severe neurological signs and symptoms with complete or partial resolution of the signs and symptoms over several weeks.

Individuals with MS often have a reduced exercise tolerance and it is usually advised that they avoid strenuous exercise, exhaustion and cold exposure. It is impossible to distinguish the signs and symptoms of MS from those of arterial gas embolism or decompression sickness. Therefore, most patients with MS should not dive.