Amoebic brain abscess is an affliction caused by the anaerobic parasitic protist '' Entamoeba histolytica''. It is extremely rare; the first case being reported in 1849. Brain abscesses resulting from '' Entamoeba histolytica'' are difficult to diagnose and very few case reports suggest complete recovery even after the administration of appropriate treatment regimen.

Signs and Symptoms

The onset of symptoms is very abrupt and the disease progression is very rapid. Hence finding the root cause of the symptoms is very important as failing to do so, could result in imminent death. Signs and symptoms include: * Prolonged

headache Headache is the symptom of pain in the face, head, or neck. It can occur as a migraine, tension-type headache, or cluster headache. There is an increased risk of depression in those with severe headaches. Headaches can occur as a result ...

s * Progressive Drowsiness * Diminished upper limb movement *

Trouble swallowing Dysphagia is difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, in some contexts it is classified as a condition in its own right. It may be a sensation that suggests difficulty in the passage of solids or liqui ...

* Breathing difficulties * Low grade fever * Intestinal symptoms The CT images for the abscesses caused by '' Entamoeba histolytica'' are completely indistinguishable from the abscesses caused by any other organisms or causative agents. However, the brain abscesses are often observed in the frontal lobe or the basal ganglial regions.

Immunopathogenesis of '' Entamoeba histolytica'' and associated complications

Once the trophozoites undergo excystation in the terminal ileum region, they colonize the large bowel, remaining on the surface of the mucus layer and feeding on bacteria and food particles. However, in response to an unknown stimuli, trophozoites often move through the mucus layer and once they come in contact with the epithelial cell layer, they are able to start the pathological process. ''E. histolytica'' has a

lectin Lectins are carbohydrate-binding proteins that are highly specific for sugar groups that are part of other molecules, so cause agglutination of particular cells or precipitation of glycoconjugates and polysaccharides. Lectins have a role in rec ...

that binds to galactose and N-acetylgalactosamine sugars on the surface of the epithelial cells. The

is normally used to bind bacteria for ingestion. The parasite has several enzymes such as pore forming proteins,

lipase Lipase ( ) is a family of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually tr ...

s, and

cysteine protease Cysteine proteases, also known as thiol proteases, are hydrolase enzymes that degrade proteins. These proteases share a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic triad or dyad. Discovered by Gopal Chund ...

s, which are normally used to digest bacteria in food vacuoles. However, these enzymes can cause lysis of the epithelial cells by inducing cellular necrosis and apoptosis when the trophozoites come in contact with them and bind via the lectin. This allows for penetration into the intestinal wall and blood vessels, sometimes leading to the liver and other organs like the brain. Meanwhile, the trophozoites begin to ingest the dead cells which triggers a massive immune response in the epithelial cell layer. The damage to the epithelial cell layer attracts immune cells, which in turn can be lysed by the trophozoite. This results in the release of the immune cells' own lytic enzymes into the surrounding tissue thus ultimately leading to excessive tissue destruction. This destruction manifests itself in the form of an ' ulcer', typically described as flask-shaped because of its appearance in transverse section. This tissue decimation can also involve blood vessels leading to bloody diarrhea or amebic dysentery. Occasionally, when the trophozoites enter the bloodstream, they are generally transported to the liver via the

portal system In the circulatory system of animals, a portal venous system occurs when a capillary bed pools into another capillary bed through veins, without first going through the heart. Both capillary beds and the blood vessels that connect them are co ...

. In the liver a similar pathological sequence ensues, leading to amebic liver abscesses. The trophozoites can also end up in other organs, as a result of liver abscess rupture or fistulas. In extremely rare cases, when the trophozoites travel to the brain surpassing the blood-brain barrier, they can cause amoebic brain abscess.

Diagnosis

The diagnosis of '' Entamoeba histolytica'' in the brain abscesses is difficult for several reasons. Firstly, the aerobic and anaerobic cultures generally provide negative results. In addition, the CT results are often inconclusive and even the parasitologic stool examinations and abdominal ultrasonography often yield normal results. However, direct examination of the abscess capsule may exhibit necrotic material, foamy histiocytes, rare eosinophills and ingested erythrocytes. Spheric structures may insinuate the presence of '' Entamoeba histolytica trophozoites with''

Masson's trichrome stain Masson's trichrome is a three-colour staining procedure used in histology. The recipes evolved from Claude L. Pierre Masson's (1880–1959) original formulation have different specific applications, but all are suited for distinguishing cells f ...

''.'' Additionally,

PCR PCR or pcr may refer to: Science * Phosphocreatine, a phosphorylated creatine molecule * Principal component regression, a statistical technique Medicine * Polymerase chain reaction ** COVID-19 testing, often performed using the polymerase chain r ...

based analysis of the CSF can be used to positively identify the parasite in the system . Combination of CT scans and PCR based identification along with the serological methods are the current diagnostic measures for detecting '' Entamoeba histolytica.''

Treatment

Metronidazole Metronidazole, sold under the brand name Flagyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis. It is ef ...

is the first choice of drug for the treatment of the abscesses caused by '' Entamoeba histolytica'' . In addition, luminal amebicides such as Paramomycin must be administered after completion of

treatment. This ensures complete eradication of the parasitic protist from the system.

References

External links