Treatment Macrolide antibiotics such as azithromicin and clarithromicin but also erythromycin and tetracycline derivatives reduce morbidity, mainly by eradicating the pulmonary infection, but the effects of antibiotics on the nervous system complications are not known.
Meningoencephalitis from this organism is most likely to occur in immunosuppressed and debilitated individuals and is a well-known and occasionally fatal cause of meningitis in the newborn. Meningitis is the usual neurologic manifestation, but there are numerous recorded instances of isolated focal bacterial infectious encephalitis, rarely with a normal CSF, most cases showing a pleocytosis that may be initially polymorphonuclear. Between 1929, when the organism was discovered, and 1962, when Gray and Killinger collected all the reported cases, it was noted that 35 percent of patients had either meningitis or meningoencephalitis as the primary manifestation.
The infection may take the form of a brainstem encephalitis, or “rhombencephalitis,” specifically with several days of headache, fever, nausea, and vomiting followed by asymmetrical cranial-nerve palsies, signs of cerebellar dysfunction, hemiparesis, quadriparesis, or sensory loss. Respiratory failure has been reported. Of 62 cases of Listeria brainstem encephalitis reported 25 years ago by Armstrong and Fung 8 percent were in immunosuppressed patients, however, in the current era 20 percent or fewer of affected patients are immunocompetent. In the elderly, no additional cause of immune disorder appears to be necessary. Meningeal signs were present in the only half the patients in the above mentioned series, and the spinal fluid often showed misleadingly mild abnormalities. CSF cultures yielded Listeria in only 40 percent of cases (blood cultures were even more often normal). Consistent with our experience, the early CT scan was often normal; MRI, however, has revealed abnormal signals in the parenchyma of the brainstem.
The monocytosis, which gives the organism part of its name, refers to the reaction in the peripheral blood in rabbits but these cells have not been prominent in the blood or CSF of patients. Judging from the clinical signs in some cases, the infection appears to affect both the brainstem parenchyma and the extraaxial portion of the lower cranial nerves. One patient described by Lechtenberg and coworkers had a proven brain abscess; other patients have had multiple small abscesses (Uldry et al) but it is not clear if this is a uniform feature of the illness that explains the rhombencephalitis.
Treatment The treatment is ampicillin (2 g intravenously q4h) in combination with gentamicin (5 mg/kg intravenously in 3 divided doses daily). If the condition of the host is compromised, the outcome is often fatal, but most of our patients without serious medical disease have made a full and prompt recovery with treatment.
In India and Southeast Asia, particularly Cambodia and Thailand, a brainstem, cerebellar, and meningitic illness, similar to that caused by Listeria, results instead from melioidosis (Burkholderia pseudomallei). A typical presentation is of multiple small abscesses with a predilection for white matter tracts of the cerebrum and cerebellum (Fig. 31-1). It should be suspected in returning travelers from that region but the disease is, of course, well known to physicians in areas endemic for the organism. Diabetics are particularly prone to this infection. The CSF shows one to several dozen white blood cells and raised protein but glucose may be normal. There is usually an associated pulmonary infection but this may be minor and the degree of temperature elevation varies. The diagnosis can be made by the culture of the organism from body sites such as CSF, pharynx, blood, urine or sputum, as it is not a normal commensal bacterium. Both blood agar and special Ashdown’s medium containing gentamicin are required for culture. There is a commercial serologic test but there are high background rates of positivity in endemic regions.