Pneumonia's link with the head and heart

In October, 2006, a 6-year-old girl presented with a month’s history of progressive right arm dystonia. Apart from the dystonia, her physical examination was normal. Baseline blood tests were normal, as was her chest radiograph. Urine, throat, and blood cultures for pathogenic bacteria and anti-streptolysin O were negative. Brain MRI showed striatal encephalitis (fi gure A), but CSF microscopy, culture, and PCR for Mycoplasma pneumoniae and common neurotropic viruses, were negative. Serum copper and caeruloplasmin, lactate (blood and CSF), very-long-chain fatty acids, lysosomal enzymes, acylcarnitines, aminoacids, urinary organic acids, ammonia, and lipid electrophoresis were all normal. However, serum titres of IgG and IgM antibodies to M pneumoniae were increased and persisted for 3 months. Doppler echocardiographic examination also showed endocarditis (fi gure B). On the basis of the positive serology, our patient was treated with ciprofl oxacin for 15 days. However, her dystonia did not improve, so two cycles of intravenous immunoglobulin were given, with partial improvement of neurological symptoms. One week later, repeat echocardiography was normal, apart from the tricuspid aortic valve; brain MRI showed a signifi cant improvement. In March, 2009, our patient still had mild right arm dystonia; complete neurological recovery was thought to be unlikely because of necrotising lesions within her brain. M pneumoniae is one of the major causes of encephalitis in children and, together with group A β-haemolytic streptococci, is recognised to be a cause of paediatric striatal encephalitis. Mycoplasma encephalitis is generally classifi ed as an early-onset (para-infectious) type, characterised by a direct invasion of CNS, or a late-onset (post-infectious) type, due to an immune-mediated process. In our patient, the negative PCR for M pneumoniae, the high antibody titres, which were stable for 3 months, the worsening of the right arm dystonia, and the MRI features of striatal encephalitis suggested a recent past infection, compatible with a post-infectious Mycoplasma encephalitis. Two immune mechanisms are theoretically involved in the CNS manifestations of M pneumoniae: a direct type, in which infl ammatory cytokines locally induced by lipoproteins contained in the bacterial cell membrane have a role; and an indirect type, in which autoimmunity, through cross-reaction between bacterial cell components and human cells has a role. Polyclonal B-cell activation as well as the production of various autoantibodies, including to brain tissue, can occur in the course of M pneumoniae infection. This activation may be non-specifi c (independent of antigen) such as in superantigen-mediated diseases, or by a mechanism of molecular mimicry. The latter mechanism is known to underlie rheumatic heart disease, caused by group A β-haemolytic streptococci. The similarity between post-infectious striatal encephalitis caused by M pneumoniae and that by group A β-haemolytic streptococci led us to do echocardiography on our patient and discover her endocarditis. Little is known about pathogenetic mechanisms of endocarditis after M pneumoniae infection; some observations suggest that it is due to a direct-type extrapulmonary manifestation of the infection, also autoimmune mechanisms might be involved. In our patient, the failure of antibiotic therapy, the improvement in her neurological symptoms, and the resolution of endocarditis after immunomodulatory treatment suggested an autoimmune pathogenesis of her complications. In addition to streptococci, M pneumoniae should be recognised as another infectious agent associated with cardiac complications.