Mycoplasma pneumoniae causing nervous system lesion and SIADH in the absence of pneumonia

A patient was admitted for fever and acute respiratory failure (ARF), rapidly progressive tetraparesis, delirium, behavioral abnormalities, and diplopia. Leukocytosis and a rise in C-reactive protein were present. A syndrome of inappropriate anti-diuretic hormone secretion (SIADH) was also diagnosed. Lumbar puncture yielded colorless CFS with mononuclear pleocytosis and protein rise. Electrodiagnosis revealed demyelinating polyneuropathy and axonal degeneration. Serum IgG and IgM for mycoplasma pneumoniae (MP) was consistent with acute infection, and erythromycin was started with rapid resolution of symptoms. Contrarily to most reports, an associated respiratory disease was not present and SIADH in association with MP has been reported only once, in a patient without direct central nervous system (CNS) involvement. Differential diagnosis and possible pathogenic mechanisms are discussed.