neurologic complications from mycoplasma pneumoniae have been known since the 1940s.1 encephalitis is the most common complication , and occurs most often in children . a review by lerer and kalavsky2 found that 53% of patients with central nervous system ( cns ) disease associated with m. pneumoniae were between the ages 6 years and 20 years . it is estimated that between 5% and 10% of acute childhood encephalitis in europe and north america is attributable to m. pneumoniae.3 there is a spectrum of clinical manifestations such as aseptic meningitis , peripheral neuropathy , transverse myelitis , cranial nerve palsies , cerebellar ataxia , acute transverse myelitis , and acute disseminated encephalomyelitis.4 the incidence of these manifestations has been estimated to be between 0.06% and 0.1%,5 but cns symptoms are reported in up to 7% of patients in the hospital setting with confirmed m. pneumoniae infection.6 long - term neurological problems have been noted in 20%60% of cases , with severe disease resulting in mental retardation , brain atrophy , hydrocephalus , epilepsy , visual changes , and global neurologic deficits with brainstem dysfunction and cerebellar ataxa.7 two studies have shown that between 24% and 30% of patients require intensive care treatment , with mortality rates of between 8% and 10%.8,9 the index patient presented with a 2-week history of head - aches , fevers , and dry cough . her examination revealed an ataxic gait with normal muscle power , reflexes , and skin sensation . initial computed tomography imaging of her brain showed a single hypodense white matter lesion in the left frontal lobe . a subsequent magnetic resonance imaging scan ( mri ) of the brain demonstrated a corresponding t2 and fluid - attenuated inversion recovery ( flair ) hyperintense lesion in the left frontal lobe ( fig . given the patient s age and symptoms , a diagnosis of multiple sclerosis was also considered . other investigations revealed a positive total m. pneumoniae serology immunoglobulin ( ig)m antibody titer of > 1,280 . the diagnosis of m. pneumoniae - related cns disease was made based on the patient s clinical symptoms , positive serology , and the mononuclear pleocytosis found in the csf . this is typically in the range of 10200 cells/l for m. pneumoniae - associated cns infections.10 routine csf gram stain and bacterial cultures are characteristically negative . one review of 58 cases showed a diagnosis was made in 84% of patients with positive serology , 14% with csf polymerase chain reaction ( pcr ) , and 2% with csf antibody determination.11 our laboratory was able to evaluate the csf for the open reading frame ( orf ) 521 nuclear capsid protein gene with pcr , which returned a negative result . acyclovir was ceased 3 days into hospital admission , and the patient was prescribed a course of oral doxycycline . the patient s symptoms resolved over a period of 1 week of observation in hospital . further analysis of the csf with isoelectric focusing revealed oligoclonal bands of igg in the csf that was not present in the serum . two subsequent cranial mri scans of the patient were obtained over a period of 3 months in the outpatient setting , and they showed the stable appearance of the left frontal lobe lesion . the positive oligoclonal bands in the csf are likely related to the immunological phenomena that are commonly linked to m. pneumoniae infections . it has been known since the 1970s that polyclonal b - cell activation and antibodies to brain tissue have been demonstrated in m. pneumoniae infections . 12 in 1996 , nishimura et al.13 reported three cases of m. pneumoniae encephalitis with associated anti - galactocerebroside antibodies . in this patient , a moderately positive anti - ganglioside gq1b antibody was found . this supports the hypothesis that demyelination and neurologic dysfunction in this entity could be mediated by the immune system . the pathogenesis of m. pneumoniae cns disease is unclear , but it may be related to direct invasion ( proven during brain biopsy culture15 or nucleic acid hybridization16 ) or autoimmunity ( immune complexes , cross - reacting antibodies , or a neurotoxin effect).17 this case highlights a rare cause of encephalitis in a patient presenting to a tertiary - level adult teaching hospital .