Infections – Diseases

Bacterial

Meningitis

Infection within the subarachnoid space
Usually caused by spread of an infectious agent via the bloodstream from an infective focus elsewhere in the body
- In neonates, 50% are from things like E coli and H influenzae
- In children, 50% are from H influenzae
- In adults, 30% are from S pneumoniae
Clinical manifestations
- Rapid onset over several days
- Clinical symptoms include generalized headache, fever, vomiting. Lethargy, stiff neck, and confusion.
- Malaise and backache are common
- Treatment is with a high-dose of intravenous antibiotics that cross the blood-brain barrier
- Neurologic Complications
  - Seizures
  - Focal cerebral signs
  - Acute cerebral edema
  - Dysfunction of cranial nerves 3, 4, 6, & 7 in about 15% of patients
  - Hearing loss
  - Hemiparesis
  - Dysphasia and hemianopsia in 15%

Brain Abscess

Causes
- Infection spread from middle ear or sinus
- In association with congenital heart disease
- Spread of infection from a distant site
- Direct introduction of bacteria following penetrating head injuries
Cardinal symptom is a relentless and progressive headache, which is usually followed by focal neurologic manifestations
Fever is seen in only two thirds of patients
Early diagnosis is possible with CT
Lumbar puncture should be avoided to prevent herniation or rupture of the abscess into the ventricular system
Treatment with penicillin or the such may be successful such that surgery may not be necessary

Neurosyphilis

Paretic neurosyphilis is the late complication of syphilis occurring decades after the original infection (there are other types of neurosyphilis)
Clinical presentation resembles meningoencephlitis
Early symptoms include fatigue, irritability, personality changes, forgetfulness, and tremor
Symptoms at late stage include impaired memory and judgment, confusion, disorientation, seizures, dysarthria, myoclonus, and poor motor control
Treatment with penicillin is the antibiotic of choice for all forms of neurosyphilis

Cysticercosis

Infection with the larval form of the porcine tapeworm
Humans acquire the adult tapeworm by eating uncooked pork
Humans also may accidentally ingest tapeworm eggs, which hatch in the small intestince, burrow into venules, and are carried to distant sites
The larvae are relatively large and may lodge in the subarachnoid space, ventricles, or brain tissue
Symptoms may not occur until 4-5 years later, when larvae die and provoke an inflammatory response
Cysts in the cerebrum may mimic a brain tumor
Cysts in the subarachnoid space may result in a chronic meningitis and arachnoiditis
Cysts in the ventricular system may cause obstructing hydrocephalus

Tetanus

Viral (HIV/AIDS discussed elsewhere)

Meningitis

Referred to aseptic memingitis
Rarely fatal
Typically runs its course
Clinical syndrome consists of fever, headache, and other signs of meningeal irritation and a predominantly lymphocytic pleocytosis with normal CSF glucose
Other symptoms may include lethargy, irritability, and drowsiness. Also may see photophobia, pain with eye movements, or stiffness of the neck and spine on forward bending (meningeal irritation)
It’s rare to see confusion, stupor, or coma

Varicella-Zoster

Varicella-Zoster is an exclusively human herpesvirus that cause chickenpox (varicella), becomes latent in cranial nerve and dorsal-root ganglia, and frequently reactivates decades later to produce shingles (zoster) and postherpetic neuralgia
Associated with severe, sharp pain and characteristic rash
Occurs more often in immunocompromised patients or the elderly
Varicella occurs mostly in the spring, but zoster develops throughout the year
Common cranial nerve involvement are 5, 7, & 3
Treatment may include analgesics (e.g., acetaminophen, codeine) and antivirals (e.g., famciclovir, oral acyclovir)

Herpes simplex encephalitis

It’s the most common sporadic acute viral disease of the brain in the U.S.
It affects both sexes and all age groups in every season
Mortality is high (70%)
Survivors often have significant neuropsychiatric sequelae
Most greatly affects the medial temporal and frontal lobes
Common to see hemorrhagic necrosis, infammatory infiltrates, and cells containing intranuclear inclusions
Most common clinical findings are fever and alteration of consciousness
In majority, we see headache, personality changes, speech difficulties, and seizures
Mortality can be substantially reduced by early antiviral therapy (e.g., Acyclovir), although cognitive deficits are permanent

Rabies

Acute viral disease of the central nervous system
Usually transmitted to humans through a wound contaminated by the saliva of a rabid animal
Rare airborne transmission has been noted in bat-infested caves
Dog and cat bites account for 90% of human rabies cases
The virus travels by nerve routes into the brain where it disseminates widely, then traveling to multiple organs
Incubation periods range from 15 days to 1 year
The disease begins with a prodrome of anxiety, fever, and headache, often with paresthesias at the bite site
2-10 days later, we see delirium, seizures, nuchal rigidity, paralysis, and excitability
Stimulus-sensitive spasms of the pharynx, esophagus, or neck muscles may occur. Survival is not great at this stage
Treatment with vaccine, but no known effective treatment once clinical illness develops