Teaching Case

Neurological disordres in an infectious context.

Fever, headaches and cranial nerve palsy in an immunocompromized patient treated for an acute leukemia. A brain stem infection is suspected on the basis of a
diphasic syndrome first characterised by fever, nausea and headache, followed,
in a second phase, by severe brain stem dysfunction at the level of the pons, with meningism, multiple cranial nerve palsies, ataxia, and seizures. The early examination of the cerebrospinal fluid demonstrats the presence of Gram-positive bacilli whose typical
characteristics were compatible with those of Listeria. An MRI is performed in the early course of the disease.

Listeria monocytogenes is a Gram-positive bacterium responsible for severe infections in human and a large variety of animal species. It is a facultative intracellular pathogen which invades macrophages and most tissue cells of infected hosts where it can proliferate.

In infected hosts, the bacteria cross the intestinal wall to invade the mesenteric lymph nodes and the blood. The main target organ is the liver, where the bacteria multiply inside hepatocytes with possible prolonged septicemia, particularly in immunocompromised hosts. Cerebral nervous parenchyma infection is seen only in about 10 % exposing to meningitis, meningoencephalitis and less frequently abscesses especially in the posterior fossa and the brain stem called rhombencephalitis.

Listeria monocytogenes rhomboencephalitis is an uncommon but very suggestive complication of listeria infection. It presents in a typical biphasic pattern characterised by a non-specific prodromal period followed by any combination of asymmetrical cranial-nerve palsies, cerebellar signs and diminished consciousness.

The prognosis of listeriosis depends on the severity of meningoencephalitis, due to the elective location of foci of infection in the brain stem. The survival rate is greater than 70% when appropriate antibiotic therapy is initiated early. However, approximately 60% of the survivors develop neurological sequels.

The radiological aspects of listeria infection to the brain are not specific to the germ.
CT can demonstrate low attenuation and poorly defined areas, which may be associated with gyriform enhancement after contrast media administration. These areas are often associated with meningitis with adjacent meningeal enhancement.
MR demonstrates non-specific images of abscess with lesions appearing hypointense on T1-weighted sequences with increased signal intensity on T2- weighted sequences. The lesions presents peripheral ring enhancement after gadolinium administration. A peri-lesionnal oedema could also be well demonstrated by MRI.
Although the radiological aspects of listeria abscess is not specific to the germ, the diagnosis of listeria rhombencephalitis is strongly suspected when the brain stem is involved during brain infection.

Since any biopsy could be performed in these deep-located infections to the posterior fossa, the diagnosis should be based on clinical, biological and bacteriological findings. An appropriate antibiotic therapy should be rapidly initiated with close monitoring in an intensive care unit.

In the present case, the diagnosis of Listeria infection was based on the clinical findings, the results of cerebrospinal fluid analysis and blood culture and on the MR findings. The treatment was started before culture results were available, and the patient had a full clinical recovery.