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Sir,

Mycoplasma pneumoniae is an atypical bacterium that can cause a great variety of respiratory infections and can be responsible for ocular involvement such as conjunctivitis, anterior uveitis, and very rarely optic neuropathy. We report a case of bilateral vision loss with optic disc swelling that developed 4 days after starting treatment for atypical pneumonia and was accompanied by multiple demyelinating brain lesions.

Case report

A 24-year-old male presented as an outpatient with a 2-day history of deterioration of vision in both eyes, headache, stiff neck, and general malaise. Owing to febrile illness accompanied by herpes labialis, he had been taking amoxicillin for a week without improvement. An infectologist diagnosed atypical pneumonia 4 days before ophthalmological examination and administered clarithromycin 500 mg b.i.d. The patient had been without fever for the preceding 3 days.

On examination, his unaided visual acuities (VA) were counting fingers (CF)/2 m right, 0.25 left. Pupillary reactions were diminished and relative afferent pupillary defect (RAPD) was absent. Fundoscopy revealed swelling of both optic discs with few splinter haemorrhages peripapillary and mildly dilated veins. Optic papillitis was diagnosed, however, because of the history of fever and meninigeal signs present, he was referred to an infectologist. Laboratory tests and a lumbar puncture were carried out. Serology was positive for M. pneumoniae (IgG >200 IU/ml; range 20–30 IU/ml, IgM 149 IU/ml, range 13–17 IU/ml), negative for Chlamydia pneumoniae, Chlamydia psittaci, Chlamydia trachomatis and Legionella pneumophila, Herpes simplex, Varicella Zoster and Epstein–Barr virus. A lumbar puncture was performed and cerebrospinal fluid (CSF) was sent for analysis. The CSF pressure was normal (14 mmH2O), total proteins were 0.38 g/l (normal range 0.15–0.45) with an increased level of immunoglobulin (Ig) M 2.2 mg/l (less than 0.7) and absent oligoclonal bands.

The patient was then reviewed in the Eye Clinic 4 days after initial examination. His vision deteriorated to no light perception in both eyes. The pupils were nonreactive and fundus appearances were unchanged. The consultant neurologist could not find other cranial nerve abnormalities or motor deficits. The patient was admitted to the Eye Clinic. Magnetic resonance imaging (MRI) demonstrated multiple round lesions located in the cerebellar pedunculum, thalamus, internal capsule, corpus callosum, and corona radiata, showing homogeneous contrast enhancement. Bilateral optic neuritis in the course of acute disseminated encephalomyelitis (ADEM) was diagnosed. Intravenous methyprednisolone (1000 mg/day) was administered for 5 days, followed by oral 60 mg Medrol in tapering doses, while still being treated with clarithromycin 500 mg b.i.d. His VA improved in the next 10 days to 0.7 right and 0.8 left, and 1.5 months later to 1.0 in both eyes. During the last examination 6 months later, VA was the same, the pupils were symmetrical, reactive, RAPD absent, but optic atrophy was noted. Visual fields in the central and nasal part showed slightly decreased retinal sensitivity in both eyes.

Comment

ADEM is a rare inflammatory demyelinating disease of the central nervous system, typically occurring after infections or vaccinations and affecting predominantly children and young adults.1 Pathogenesis of ADEM is not known; an autoimmune response mediated by autoreactive T lymphocytes with specificity for myelin antigens (such as myelin basic protein) triggered by infection or immunization is considered to be a possible aetiological factor.2 Characteristic clinical features include sudden onset of multifocal neurological disturbances such as bilateral optic neuritis, aphasia, motor and sensory deficitis, ataxia and signs of an acute meningoencephalopathy with meningismus, seizures, and psychosis.

As in the case highlighted here in, MRI reveals single or multifocal areas of increased signal intensity on T2-weighted sequences predominantly in white matter, but gray matter can also be affected, particularly basal ganglia, thalami, and brainstem. CSF can be normal, but often shows pleocytosis and only rarely intrathecal oligoclonal IgG production. In this case, there was increased intrathecal synthesis of IgM which was also found in 25% of adult patients with ADEM.3

Milla et al4 reported a case of severe visual loss following M. pneumoniae pneumonia accompanied by single MRI lesion in the white matter with good visual recovery. The authors concluded that optic neuropathy occurring in a young patient within a few days after a febrile illness and especially pneumonia appeared characteristic enough to suggest infection with M. pneumoniae. Bilateral optic neuritis has been described as a common finding in ADEM,5 but was found only in one out of 40 adults diagnosed as ADEM.3 In the same study, 35% of patients experienced a second clinical episode during the mean follow-up of 38 months and were finally diagnosed as MS. Patients with ADEM were younger, and a preceding infection was present significantly more often than in patients with MS. As fever and infection are also well-known trigger factors for MS attacks, the presence of prior infection cannot reliably distinguish a first episode of MS from monophasic ADEM. Also the MRI findings cannot differentiate ADEM from MS.5

Most patients with ADEM had a favourable outcome.5 At follow-up examinations, 49% were without symptoms, 35% had minor nondisabling symptoms, and 12% had moderate deficits. Among patients with MS (ADEM converting to MS), only two (14%) were without symptoms.

No therapy has been established by controlled clinical trials and spontaneous improvement has been repeatedly noted.6 Most authors report favourable response to corticosteroids, especially pulsed intravenous steroids with an oral taper.

In this particular case, sudden onset of bilateral neuritis following infection, MRI changes, and complete recovery are indicative for ADEM. For definite diagnosis to confirm a monophasic course, follow-up is necessary, as more than one-third of the patients initially diagnosed as ADEM converted to MS.