Intro to Infectious Disease

Question 1

CNS infections typical symptoms

Answer 1

Fever, headache, altered mental state

Question 2

encephalitis vs encephalopathy

Answer 2

encephalopathy refers to diffuse cerebral dysfunction without
inflammation usually due to toxin or metabolic dysfunction, headaches, fever, and seizures are common

encephalitis: headaches, fevers and seizures are common

Question 3

Why are CNS infections uncommon?

Answer 3

Scalp and skull protect from external entry

Three meninges (dura mater, arachnoid, pia mater) surround brain and spinal cord

Epidural abscess are limited due to tight attachment of dura to periosteum.

Tight junctions of blood-brain barrier prevent organisms from entering CNS

Question 4

Microbial mechanisms of invasion of brain

Answer 4

Hematogenous dissemination
Contiguous spread from sinusitis, otitis media, mastoiditis
Trauma or congenital lesions
Retrograde axonal transport

Question 5

Meningitis location

Answer 5

subarachnoid space

Question 6

Encephalitis location

Answer 6

diffuse parenchyma

Question 7

Abscess location

Answer 7

focal parenchyma

Question 8

Myelitis location

Answer 8

Myelitis

Question 9

immediate treatment for CNS infections

Answer 9

History and physical
Blood culture and EMPIRIC TREATMENT
Neuroimaging
Lumbar puncture/biopsy
Identify organism (Gram stain/PCR/RT-PCR)
Antibiotic susceptibility testing
Switch to definitive treatment and/or supportive therapy

Question 10

Important parts of a history

Answer 10

Season- Enterovirus, most common cause of viral meningitis and encephalitis,
occur primarily in late summer to fall
Geography- Tick exposure, West Nile virus

Question 11

TORCH infections

Answer 11

Mild maternal morbidity, but have serious fetal consequences
Meningitis: Group B strep, E. coli, Listeria
TORCH, which includes Toxoplasmosis, Other (syphilis, varicella-zoster, parvovirus B19), Rubella, Cytomegalovirus (CMV), and Herpes infections (HSV-2)

Empiric antibiotics if suspect bacterial meningitis covering most likely agents
Take blood culture first
Bactericidal- 10 fold greater than minimum inhibitory concentration
BBB effects penetration and characteristics of the drug
Antibiotic susceptibility testing

Question 12

Empiric treatment includes…

Answer 12

3rd generation cephalosporins

Bactericidal, small, lipophilic, low affinity for plasma binding proteins, and not a ligand of the efflux pumps at the blood brain barrier.

Newborns and individuals with CNS inflammation have increased penetration, and can give steroids to make drugs more effective

Question 13

relationship between drug effectiveness and neurotoxic side effects?

Answer 13

Generally, the better the drug, the higher risk of neurotoxic side effects

Question 14

Neuroimaging

Answer 14

CT/MRI

View mass lesions not helpful for meningitis

Risk factors: trauma, immunocompromised, focal neruologic findings, or decreased consciousness

If focal mass lesion, then lumbar puncture should not be done because of risk of brain herniation due to very high intracranial pressure.

Question 15

lumbar punctures

Answer 15

don’t do if there is high pressure: you might cause the brain to get sucked through the spinal cord, be generally familiar with viral vs bacterial results

Question 16

Meningitis

Answer 16

subarachnoid space

95% have 2 out of headache, fever, nuchal rigidity, and altered mentality
Viral (most common), Bacteria (life-threatening)
Fungi, Protozoa (immunocompromised)
Pathogens effect different age groups
Virulence factors like capsules allow pathogens to evade immune system
Vaccines are available against several of the strains of life-threatening bacteria.

Question 17

Encephalitis

Answer 17

diffuse infection of parenchyma

Fever, headache, and alteration of mental status
Motor and sensory deficits not seen in meningitis
Progression to seizures, speech disturbances, lethargy and coma
33%-66% of cases etiology is unknown despite an extensive diagnostic workup
Viral: Enterovirus, Arbovirus, Herpes virus, Rabies
Nonviral: Rickettsia, Mycoplasma, Acute desseminated encephalomyelitis
Empiric treatment with acyclovir until HSV ruled out.

Question 18

Brain abscess

Answer 18

focal infection of parenchyma

Symptoms: Fever, headache, neurologic defects, seizure
Pre-existing ischemia, necrosis begins as cerebritis and then becomes encapsulated.
Can be caused by a mixture of bacteria: Streptococci (most common), Pseudomonas, Haemophilus, Staphylococcus, Bacteroides
Mycobacterium, fungi, or parasites (immunocompromised)
Otitis media>temporal lobe/cerebellum
Dental/sinus infection>frontal lobe
Hematogenous>multiple, territory of middle cerebral artery
Trauma

Diagnosis: CT and MRI scans including needle aspiration to culture organism (only 10% of blood cultures are positive)
No lumbar puncture- not beneficial and risk of herniation
Treatment: Ceftriaxone + Metronidazole (parasites) and may require surgery if Staphylococci (vancomycin) and if Pseudomonas (ceftazidime)
Rupture and cause meningitis

Question 19

Myelitis

Answer 19

Herpesviruses (HSV, CMV, EBV, and VZV) are associated with myelitis which results in motor weakness and sensory loss.
Polio virus, Coxsackie virus, and West Nile virus can attack anterior horn cells and cause motor paralysis.
Chronic myelopathy is associated with Tropical Spastic Paraparesis caused by Human T-lymphotropic virus (HTLV-1)