Chapter 23: Infections of the nervous system Flashcards
Through which routes may infectious agents reach the nervous system?
- Hematogenous spread by way of the arterial blood supply (most common)
- Direct implantation of microorganisms is almost invariably due to open or penetrating trauma; (rarely iatrogenic, by a lumbar puncture needle or into a surgical field)
- Local extension can occur with infections of the skull or spine (sources include air sinuses, infected teeth, cranial or spinal osteomyelitis, and congenital malformations)
- Peripheral nerves also may serve as paths of entry for a few pathogens—in particular, viruses such as rabies and herpes zoster.
True/false: The epidural and subdural spaces can be involved by viral infections, usually as a consequence of direct local spread
False! They are usually involved in bacterial or fungal infections (instead of viral)
True/false: The underlying arachnoid and subarachnoid spaces usually are unaffected, but a large subdural empyema may produce a mass effect
True
What clinical symptoms do most patients with epidural and subdural infections present with?
Most patients are febrile, with headache and neck stiffness, and if untreated may develop focal neurologic signs referable to the site of the infection, lethargy, and coma
True/false: even if an infected patient is treated with promptly, a thickened dura may be a residual finding
No, if treated prompt, complete recovery is usual (although it can occur is resolution is complete)
What is meningitis?
Meningitis is an inflammatory process involving the leptomeninges within the subarachnoid space; if the infection spreads into the underlying brain, it is termed meningoencephalitis
Does meningitis mean there is an infection?
Not per definition, chemical and carcinomatous meningitis can also occur. However infectious meningitis is most common
Infectious meningitis can be broadly divided into acute pyogenic (i), aseptic (ii) and chronic (iii) subtypes. What do i-iii mean?
i (acute pyogenic): usually bacterial
ii (aseptic): usually viral
iii (chronic): usually tuberculous, spirochetal or fungal
How are the various causes of meningitis distinguished?
Examination of CSF
What are symptoms of patients with acute pyogenic (bacterial) meningitis?
Across ages, patients typically show systemic signs of infection along with meningeal irritation and neurologic impairment, including headache, photophobia, irritability, clouding of consciousness, and neck stiffness
DON’T LEARN THIS
What are the common bacteria that are cause of acute pyogenic meningitis?
The most likely causes of bacterial meningitis vary with patient age. In neonates, common organisms are Escherichia coli and group B streptococci. In adolescents and young adults, Neisseria meningitidis is the most common pathogen; in older adults, Streptococcus pneumoniae and Listeria monocytogenes are more common
What will a lumbar puncture and CSF of bacterial/acute pyogenic meningitis reveal?
Lumbar puncture: an increased pressure
CSF: Abundant neutrophils, elevated protein, and reduced glucose
True/false: untreated pyogenic meningitis is fatal
Often yes, but with prompt diagnosis and administration of antibiotics, most patients can be saved.
What are clinical difference between acute pyogenic and viral meningitis?
The clinical course is less fulminant than in pyogenic meningitis and is typically self-limiting
What does the CSF of viral meningitis show?
Lymphocytosis, moderate protein elevation, and a normal glucose level, but bacteria cannot be cultured
Can a virus be identified by culture and serologic methods?
No, it is often difficult
(application of nucleic acid sequencing has the potential to change our understanding of these cases. There are no distinctive macroscopic findings except for brain swelling, which may be seen in only some instances. On microscopic examination, there is either no recognizable abnormality or a mild to moderate leptomeningeal lymphocytic infiltrate)
How will tuberculous meningitis appear (both clinically as morphologically)?
Tuberculous meningitis usually manifests with generalized signs and symptoms of headache, malaise, mental confusion, and vomiting. There is only a moderate increase in CSF cellularity, with mononuclear cells or a mixture of polymorphonuclear and mononuclear cells; the protein level is elevated, often strikingly so, and the glucose content typically is moderately reduced or normal
True/false: Several pathogens, including mycobacteria, some spirochetes, and fungi, cause a chronic meningitis; infections with these organisms also may involve the brain parenchyma.
True
What is neurosyphilis?
Tertiary stage of syphilis
I don’t think this is necessary to know
How can spirochetal infections appear?
don’t think you ought to know this
- Meningovascular neurosyphilis
- Paretic neurosyphilis
- Tabes dorsalis
(the differences are mostly the locations)
What is neuroborreliosis?
don’t think you ought to know this
Neuroborreliosis refers to involvement of the nervous system by the spirochete Borrelia burgdorferi, the causative agent of Lyme disease. Neurologic signs and symptoms are highly variable and include aseptic meningitis, facial nerve palsies, mild encephalopathy, and polyneuropathies.
Can fungal infection of the nervous system give rise to chronic meningitis?
Yes
Can all pathogens of infectious meningitis be associated with parenchymal infection?
Yes
What are several fungal pathogens that cause CNS disease?
don’t think you ought to know this
- Cryptococcus neoformans
- Histoplasma capsulatum
- Coccidioides immitis
Fill in: In general, viral infections are diffuse/localized, bacterial infections (not associated with meningitis) are diffuse/localized
diffuse and localized respectively
Is brain abscess often caused by viral or bacterial infections?
Bacterial
What are abscesses?
Abscesses are discrete destructive lesions with central liquefactive necrosis surrounded by a rim of vascularized granulation and fibrous tissue
What is viral encephalitis?
Viral encephalitis is a parenchymal infection of the brain that is almost invariably associated with menin- geal inflammation (meningoencephalitis)
Different viruses of viral encephalitis can show varying patterns of injury, what are the most characteristic histologic features?
perivascular and parenchymal mononuclear cell infiltrates, microglial nodules, and neuronophagia. Certain viruses also form characteristic inclusion bodies.
True/false: viral encephalitis infect any type of cell
Some viruses infect specific CNS cell types, while others preferentially involve particular brain regions
What viruses is the nervous system particularly susceptible to?
e.g. rabies- and poliovirus
Just read the following flashcards, don’t study s.v.p.
Intrauterine viral infection following transplacental spread of rubella and CMV may cause destructive lesions, and Zika virus causes developmental abnormalities of the brain. In addition to direct infection of the nervous system, the CNS also can be injured by immune mechanisms after systemic viral infections.
In the book, arboviruses, herpesviruses, cytomegalovirus, poliovirus, rabies virus, HIV and polymavirus are explained in great detail on p865-867
They are not included in these flashcards, since they aren’t discussed in the lecture. However, they are listed in the course guide so feel free to look at those pages :)
What is Progressive multifocal leukoencephalopathy (PML)?
Progressive multifocal leukoencephalopathy (PML) is caused by JC virus, a polyomavirus, which preferentially infects oligodendrocytes, resulting in demyelination as these cells are injured and then die
What clinical aspects do patients with PML present with?
Patients develop focal and relentlessly progressive neurologic signs and symptoms, and imaging studies show extensive, often multifocal lesions in the hemispheric or cerebellar white matter.
What do fungal infections produce?
Parenchymal granulomas or abscesses, often associated with meningitis (different types are not discussed)
Other meningoencephalitides (cerebral toxoplasmosis, cysticercosis, amebiasis) are also not discussed
But feel free to look at p868
What are prion diseases?
Prion diseases are a group of infectious diseases in which the causative agent is an abnormal form of a cellular protein. These include sporadic, familial, iatrogenic, and variant forms of Creutzfeldt-Jakob disease (CJD), as well as animal diseases such as scrapie in sheep and bovine spon- giform encephalopathy in cattle (“mad cow disease”)
further info (p869-890) are skipped because they’re also not explained in the lecture
