Multiple sclerosis (MS) is the most common cause of mental and physical disability in young adults affecting approximately 10'000-15'000 persons in Switzerland (incidence 16/100000; prevalence 190/100000). MS-fatigue affects at least 75% of the MS-patients (affected persons in Switzerland 7500-11250). MS-related fatigue has socioeconomic consequences leading to increased sick leaves and a higher probability of unemployment. Effective treatment strategies for MS-fatigue are missing, despite the appearance of more effective immunotherapies to treat autoimmune neuroinflammation and to control MS disease activity. The reason for the lack of therapeutic options is the unclear pathophysiological mechanism of fatigue with many non-MS associated influencing factors like thyroid dysfunction and anaemia.~Fatigue is also present in other inflammatory diseases, cancers and immunodeficiency syndromes. Regarding the latter patients with primary immunodeficiencies (PIDs) and common variable immunodeficiency (CVID) suffer from fatigue in 30 - 76%, which is more common than in the normal population. Studies investigating immunoglobulin replacement therapy in patients with CVID demonstrated a correlation between the frequency of infusions / s.c. applications and wear-off effect/fatigue.~Immunoglobulin deficiency seems to be much more common in people with autoimmune diseases. In MS reduced serum immunglobulin G (IgG) concentrations regardless of immunotherapy affect between 8 - 26% of the patients. Nonetheless consequences of IgG hypogammaglobulinemia in MS are partly unknown. However, based on the findings in patients with CVID, fatigue might be one of them. To close this knowledge gap prospective observational studies are needed.
The investigators hypothesize that hypogammaglobulinemia (defined as IgG serum concentration <7.0g/L) is a treatable cause of fatigue in people with MS:~The primary objective is to prove the link between hypogammaglobulinemia and fatigue in patients with multiple sclerosis.~The secondary objective is to show that fatigue is mediated via frequent infections in people with MS and hypogammaglobulinemia.