Coccidioidal meningitis

Coccidioidal meningitis refers to central nervous system involvement of the dimorphic fungus Coccidioides spp, mainly Coccidioides immitis and Coccidioides posadasi.

For a general discussion, and for links to other system specific manifestations, please refer to the article on coccidioidomycosis.

Epidemiology

Coccidioidomycosis is endemic to many parts of North, Central, and South America . It usually only manifests as coccidioidal meningitis if the patient is immunocompromised, and even then, only in less than 20% of cases of disseminated coccidioidomycosis.

Clinical features

The most common symptom is headache, present in 75% of patients . It is worth noting that patients with pulmonary coccidioidomycosis may also have a headache (20%), but this tends to not be persistent, severe, or progressively worsening as it is in coccidioidal meningitis .

Other clinical features include nausea, vomiting, visual changes (including those of papilledema), mental status changes, and cranial nerve palsies . Unlike bacterial or viral meningitis, clinical signs of meningeal irritation are often absent .

These features are in addition to the pulmonary and extra-pulmonary signs and symptoms of coccidioidomycosis. It should be noted that coccidioidal meningitis, being a manifestation of disseminated or extrapulmonary coccidioidomycosis, is an AIDS-defining illness.

Pathology

The overall pathology of coccidioidomycosis is discussed elsewhere (see coccidioidomycosis and Figure 1). Coccidioidal meningitis results from haematogenous spread of endospores from the lungs.

Radiographic features

Coccidioidal meningitis has numerous imaging features and complications, including secondary hydrocephalus, vasculitis and associated subarachnoid hemorrhage and deep cerebral infarction, and cerebral or spinal abscesses . MRI is generally considered to be superior in detecting these features when compared to CT .

MRI

The classic finding on brain MRI is leptomeningeal enhancement on post-gadolinium images that is characteristically localized to the basal cisterns , but can also be diffuse . This enhancement may also extend inferiorly along the spinal cord . Interestingly, these areas of leptomeningeal enhancement may have low signal on T2-weighted imaging, perhaps as a result of accompanying hemosiderin from accompanying subarachnoid bleeding .

Accompanying this enhancement may be evidence of vasculitis including subarachnoid hemorrhage around the basal cisterns , or infarction (see ischemic stroke for MRI appearances) involving deep perforating artery territories in structures of the brain such as those located in the thalamus, basal ganglia, cerebellum, and brain stem . Focal leptomeningeal enhancement may be appreciated around the parent artery . Cortical infarction can also occur but is considered far less common .

Secondary communicating hydrocephalus has been appreciated in 70-90% of patients , but may be absent in imaging at initial presentation . Abscesses, either cerebral or spinal, may also be uncommonly present and are radiographically indistinguishable from pyogenic abscesses .

Treatment and prognosis

The mainstay of medical treatment of coccidioidal meningitis is with antifungal agents such as fluconazole . A neurosurgical consult may also be warranted for patients with hydrocephalus or cerebral abscesses, where a shunt may be needed for decompression in the former . Without treatment, prognosis is very poor, with 95% of patients not surviving more than two years .