Co-morbidity means having more than one disease or condition at the same time. Co-morbidities are common among people with MS. One US survey reported that 77% of respondents had at least one other condition alongside their MS. The most common co-morbidities include depression, raised lipid (fat) levels in the blood, anxiety, hypertension and chronic lung disease.

If you have other conditions alongside your MS, it could make treating your MS more complicated, and make it more likely that you will need hospital treatment. Co-morbidities can influence the decisions you and your team make about the medicines or therapies that are appropriate for you. For example, if you are taking medication for other conditions that you have, your MS team will need to take that into account when they prescribe medication for your MS. 

As a result of co-morbidities, you may find you are experiencing a higher burden of disability and being assessed as having a higher EDSS score.

Co-morbidities can be completely coincidental and unrelated to each other. A person with MS could develop a condition that is not related to MS or their symptoms, such as hayfever.

Alternatively, co-morbidities can result from an existing disease, or share the same risk factors. For example, urinary tract infections can be more common in people with MS if they have bladder problems. Smoking is a risk factor for MS, but is also a risk factor for hypertension or cardiovascular problems. A smoker with MS may therefore be likely to have several co-morbidities. 

There is a grey area where it is debatable whether a condition is part of MS or a co-morbidity. An example could be depression, where it could be directly due to lesion damage to the brain, or be triggered by low quality of life and the experience of living with MS. However, the reality for many people with MS is a set of complex health needs that all need to be addressed.