Fungal Infections of the Nervous System

While no infection is welcome, fungal infections are uniquely dangerous and can be difficult to diagnose and treat. This is particularly the case when the fungus invades the brain.

Fungal infections of the central nervous system are not particularly common, but when such infections occur, the results can be devastating.

The following is not a complete list of all fungal infection, but a review of the most common ones.

Aspergillus

Aspergillus species are numerous in nature as a common mold. Despite frequent exposure, human infection with Aspergillus is relatively uncommon, unless the immune system has been suppressed. Risk factors for a suppressed immune system include diabetes, steroid treatment, organ transplants, cancers, trauma, malnutrition, and AIDS, among others.

The organism enters the body after being inhaled into the lungs, where it enters the bloodstream. Once in the blood, Aspergillus can infect many different organs, including the brain.

On imaging, an Aspergillus infection causes an abscess that looks like a cannonball in the brain. Treatment is with an antifungal agent such as voriconazole or amphotericin.

Treatment can sometimes be given directly into the brain via a delivery technique called intrathecal access. Even with treatment, the mortality of this infection is relatively high.

Candida Albicans

Almost everyone is already harboring Candida in the body; it’s part of the normal flora of the gastrointestinal and genitourinary tracts. Sometimes an event happens that causes Candida to outgrow its normal boundaries, which can cause a vaginal yeast infection. Candida is also well known for causing thrush, a whitish coating of the mouth and throat.

In immunocompromised patients, Candida species may enter the blood and spread to various areas in the body. Candida may cause meningitis, most often in premature neonates, or as a surgical complication. Diagnosis is made by gathering a large amount of cerebrospinal fluid (CSF) to grow in a lab culture.

Coccidioides Immitis

Coccidioides is found in the deserts of the Southwestern United States and Central and South America. Infection with Coccidiosis can cause numerous problems, ranging from the usually benign valley fever to lethal meningitis.

If not treated, approximately 95% of patients with coccidial meningitis will die within two years, according to the National Institutes of Health.

Symptoms include a severe headache, as well as other symptoms that may not be present until late in the course of the disease.

The diagnosis of coccidial meningitis is best done by examination of CSF, obtained by a lumbar puncture. Antibodies for the organism can be tested for using that CSF. On rare occasions, a biopsy of the tissues surrounding the brain (meninges) may be needed for an accurate diagnosis.

The preferred treatment for Coccidiosis infections is oral fluconazole. Some doctors will add amphotericin B. If fluid buildup in the brain (hydrocephalus) is present, a shunt may be necessary as well. It may take weeks before there is any obvious improvement.

Cryptococcus Neoformans

Cryptococcus enters the body through the lungs after someone breathes in a fungal spore. From there, the fungus enters the bloodstream and spreads through the body, particularly to the brain. This is especially the case in people whose immune systems are suppressed, though occasionally healthy people also are infected by Cryptococcus.

Cryptococcal meningitis can be diagnosed by running appropriate tests on cerebrospinal fluid collected by a lumbar puncture. If the pressure of the CSF is measured, it can be very high in these infections.

An MRI frequently shows no changes, though sometimes a mass may be present. A blood test can also be done in patients for a cryptococcal antigen that can be useful in making this diagnosis.

Histoplasmosa

Histoplasma is a fungus that may be found in normal, healthy people—but it also occasionally causes serious illness termed histoplasmosis. In the United States, it’s usually found in the Ohio and Mississippi River valleys in the midwestern states. Outbreaks can occur in people who are exposed to large amounts of disturbed bird or bat droppings.

Most of the time, the fungus only causes problems in people whose immune systems are compromised by conditions like AIDS or certain medications. Histoplasmosis can cause fever, weight loss, and fatigue.

While Histoplasma can cause problems throughout the body—especially the lungs—when it attacks the central nervous system, it can be detected by searching for antigens in cerebrospinal fluid.

The organism does not seem to grow easily in a laboratory. Half of the time, cultures of CSF do not grow the organism, even if there is an infection. Sometimes, a brain or meningeal biopsy is the only way to make the diagnosis.

Amphotericin B is the recommended treatment for those patients sick enough to be hospitalized. Those who are less severely ill may be better treated with itraconazole, another anti-fungal.

Mucormycosis

Also known as black fungus, Mucormycosis is one of the most feared neurological infections. When a fungal infection caused by a group of molds called mucomycetes invades the brain or important blood vessels around the brain, the mortality rate is very high. Only a few patients have ever been cured under these conditions.

As soon as the diagnosis of mucormycosis is made, a surgeon is required in order to cut away all dead tissue. This surgery can be disfiguring, as the nasal cartilage, the orbit of the eye, and the palate may all have to be removed.

The fungi that cause these infections, mucomycetes are actually commonly found in nature and all humans are regularly exposed. Like many fungal infections, almost all human cases of invasion occur when the patient is immunocompromised.

Early initiation of a strong anti-fungal agent such as amphotericin B is critical. Even with aggressive treatment, survival of such invasive cerebral mucormycosis is low.

In combination with anti-fungals, early surgical intervention is required to remove as much infected tissue as possible. Depending of the extent of the infection, surgery can be disfiguring.

Rarely, the fungus can reach the brain through other routes, such as after being injected into the bloodstream with intravenous drugs.

As soon as the diagnosis of mucormycosis is made, a surgeon is required in order to cut away all dead tissue. This surgery can be disfiguring, as the nasal cartilage, the orbit of the eye, and the palate may all have to be removed.

Early initiation of a strong anti-fungal agent such as amphotericin is also critical. Even with aggressive treatment, survival of such invasive cerebral mucormycosis is rare.