Mycoplasma pneumoniae causes upper and lower respiratory-tract disease. In addition, extra-pulmonary diseases
may occur at the same time as the pulmonary infection or soon after. These complications may involve neurological,
dermatological, musculoskeletal, cardiovascular, gastrointestinal, renal and hematological systems, or more than one of
these. Complications which are dermatological, musculoskeletal and gastrointestinal are seen most frequently (15-50%)
but are not as serious as nervous, cardiac and blood disorders. The mechanism behind the development of these complications
is largely immunological. The extent to which autoimmune phenomena are responsible varies, evidence for this being
greatest for hematological disorders and least for gastrointestinal ones.