Autonomic failure in multiple sclerosis, complication or precursor?

Autonomic nervous system abnormalities are being increasingly recognized as an important aspect of multiple sclerosis (MS) on a clinical, neurophysiological and molecular level. Autonomic dysfunction in MS shows a distinctive pattern: the disease activity (manifested with relapses and MRI activity) is associated with sympathetic nervous system dysfunction, while the disease progression (manifested by increasing neurological disability) is associated with parasympathetic nervous system dysfunction, with highest percentages of involvement seen in advanced progressive MS. Furthermore, in MS, not only that autonomic symptoms are present, but may influence the disease course. A recent study has shown that presence of autonomic symptoms increase the risk of the second relapse after the diagnosis of clinically isolated syndrome by 2.7 folds. On the other hand, there is evidence suggesting that multiple sclerosis (MS) starts years before the first clinical presentation, and this period has become known as the MS prodrome. This period can span for more than a decade and the most well characterized symptom of it lies in the spectrum of autonomic nervous system abnormalities. Autonomic symptoms before the diagnosis increase the risk for the first clinical manifestation of MS, and if they are present at the diagnosis of MS, they increase the likelihood of the second relapse. All this data, emphasize the importance of studying ANS involvement in MS.