Post-polio syndrome : analysis of inflammation and immune modulation

Abstract: Poliomyelitis is a viral infection, which affects the anterior horn cells of the spinal cord leaving patients with different levels and distribution of muscle weakness and loss of, or decreased, function. This situation has previously been regarded as a stable condition. However, following recovery from poliomyelitis, with or without remaining symptoms and after a stable period, some polio patients may develop Post-polio Syndrome (PPS), a syndrome characterized by new or increasing muscular weakness, pain, fatigue, and sensitivity to cold. The findings of increased cytokine levels in cerebrospinal fluid and peripheral blood has led to the conclusion that there is an inflammatory process underway in PPS. One of the most common symptoms, in addition to muscle weakness, is pain and some earlier studies have presented evidence of an inflammatory process in muscle. This was confirmed in this research based on the findings of an elevated expression of the enzymes in the Prostaglandin E2 (PGE2) pathway, i.e. mPGES-1, COX-2, COX-1 and cPGES. This may explain muscle pain and opens new perspectives for specific treatment. It has been speculated that the inflammation in PPS may have an autoimmune background. In this research there were no circulating immune complexes in the blood of the PPS patients. This reduces the possibility that the inflammation is driven by a complement mediated autoimmune process. In some chronic inflammatory conditions there is an increase of blood lipids. In earlier studies of PPS patients, blood lipid levels have been found to be increased. In this study the blood lipids were normal, and thus, the inflammation does not appear to give rise to hyperlipidaemia. The inflammation in PPS patients is down-regulated by immune-modulatory treatment, by means of IvIg, which is followed by a clinical improvement. However, it has been difficult to pinpoint and characterize responders and non-responders. When re-evaluating the PPS diagnosis 2-8 years after the treatment, patients still considered as suffering from PPS experienced a better outcome of the treatment than patients with a stable condition, i.e. non- PPS. This opens up for speculation that PPS may be divided into two different subgroups, unstable patients with PPS driven by an inflammatory process and stable patients with a slower deterioration possibly due to ageing and concomitant disorders.