CNS Infections​

Encephalitis is inflammation of the brain parenchyma caused by an infection, usually viral. Encephalitis may present with mild symptoms such as headache, fever, fatigue, and muscle and joint pain or with severe symptoms such as seizures, altered consciousness, and paralysis. The diagnosis is based on clinical suspicion, and once suspected, immediate empiric treatment is warranted to prevent catastrophic and long-term neurologic sequelae. Encephalitis is managed with supportive measures and antiviral therapy. Focal neurologic defects are common after encephalitis; hence, physiotherapy is usually required.

Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Diagnosis of meningitis is made on clinical grounds with a thorough neurologic examination. CSF analysis is an important diagnostic tool, as it is difficult to identify the exact cause clinically. Management of meningitis includes immediate broad-spectrum antibiotics and supportive therapy to prevent complications. Specific treatment depends on the etiology of meningitis. Delay in treatment can lead to permanent neurologic defects and death.

Brain abscess is a life-threatening condition that involves the collection of pus in the brain parenchyma caused by infection from bacteria, fungi, parasites, or protozoa. The most common presentation is headache, fever with chills, seizures, and neurological deficits. Diagnosis is mainly based on imaging, as it is difficult to arrive at a definitive diagnosis based on clinical presentation alone. Management includes administration of empiric antibiotic therapy and surgical intervention. Immediate management is necessary; otherwise, severe neurologic complications ensue.

Brain abscess is a life-threatening condition that involves the collection of pus in the brain parenchyma caused by infection from bacteria, fungi, parasites, or protozoa. The most common presentation is headache, fever with chills, seizures, and neurological deficits. Diagnosis is mainly based on imaging, as it is difficult to arrive at a definitive diagnosis based on clinical presentation alone. Management includes administration of empiric antibiotic therapy and surgical intervention. Immediate management is necessary; otherwise, severe neurologic complications ensue.

Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Passing proglottids in the stool is the most common sign of taeniasis. A patient who ingests T. solium eggs can develop cysticercosis, which may present with muscular and dermatologic cysts, ocular involvement, or neurologic manifestations (neurocysticercosis). The diagnosis is made by identifying proglottids or eggs in the stool. Characteristic findings on CT or MRI will help diagnose neurocysticercosis. Management generally includes anthelmintic therapy.

Meningitis is inflammation of the meninges, the protective membranes of the brain, and spinal cord. The causes of meningitis are varied, with the most common being bacterial or viral infection. The classic presentation of meningitis is a triad of fever, altered mental status, and nuchal rigidity. Diagnosis of meningitis is made on clinical grounds with a thorough neurologic examination. CSF analysis is an important diagnostic tool, as it is difficult to identify the exact cause clinically. Management of meningitis includes immediate broad-spectrum antibiotics and supportive therapy to prevent complications. Specific treatment depends on the etiology of meningitis. Delay in treatment can lead to permanent neurologic defects and death.

Herpes simplex virus (HSV) is a double-stranded DNA virus belonging to the family Herpesviridae. Herpes simplex virus commonly causes recurrent infections involving the skin and mucosal surfaces, including the mouth, lips, eyes, and genitals. Typical mucocutaneous infections are characterized by an acute localized appearance of clusters of small, painful vesicles on an erythematous base. Although overlap exists, HSV-1 is classically associated with oropharyngeal lesions, whereas HSV-2 is mostly responsible for genital herpes, an STI. Systemic and severe infections including encephalitis, meningitis, and neonatal herpes may also occur. The diagnosis is made based on clinical presentation and history, which can be confirmed by the microscopic examination of a stained smear of a fresh vesicle, nucleic amplification test using PCR, direct immunofluorescence, or serologic tests. The therapy for mucocutaneous lesions is usually symptomatic, but antiviral therapies involving acyclovir, valacyclovir, or famciclovir are useful if given early, and are always part of the therapy for serious systemic infections.

Cryptococcosis is an opportunistic, fungal infection caused by the Cryptococcus species. The principal pathogens in humans are C. neoformans (primary) and C. gattii. Cryptococcus neoformans is typically found in pigeon droppings and acquired by inhaling dust from contaminated soil. The majority of affected patients are immunocompromised. Patients with AIDS, chronic steroid use, and organ transplant are particularly affected. The primary virulence factor is an antiphagocytic capsule, consisting of repeating capsular polysaccharide antigens. The infection typically affects the lungs and presents as a primary lesion or pneumonia. Dissemination can occur to involve the brain and meninges, skin, bones, and visceral organs. Treatment for cryptococcal meningitis is usually amphotericin B and flucytosine, followed by fluconazole. Cryptococcosis is an AIDS-defining illness and typically associated with CD4 count < 100 cells/μL.

Encephalitis is inflammation of the brain parenchyma caused by an infection, usually viral. Encephalitis may present with mild symptoms such as headache, fever, fatigue, and muscle and joint pain or with severe symptoms such as seizures, altered consciousness, and paralysis. The diagnosis is based on clinical suspicion, and once suspected, immediate empiric treatment is warranted to prevent catastrophic and long-term neurologic sequelae. Encephalitis is managed with supportive measures and antiviral therapy. Focal neurologic defects are common after encephalitis, and hence, physiotherapy is usually required.

Toxoplasmosis is an infectious disease caused by Toxoplasma gondii, an obligate intracellular protozoan parasite. Felines are the definitive host, but transmission to humans can occur through contact with cat feces or the consumption of contaminated foods. The clinical presentation and complications depend on the host’s immune status. Patients who are immunocompetent usually have no symptoms, whereas those who are immunocompromised may develop CNS toxoplasmosis or chorioretinitis. The diagnosis is often made based on serology or PCR. Patients who are immunocompetent may not need any treatment. Patients who are immunocompromised or those with severe disease may require combination therapy with pyrimethamine, sulfadiazine, and leucovorin.