Infections of Nervous System Flashcards
Give a general description of Meningitis
Microbes carried in blood or lymph can cross the Blood Brain Barrier and infect the Meninges.
- Can be caused by nearly all infective agents:
Bacteria, viruses, fungi, protozoa etc. - Can occasionally be caused by non-infectious agents:
Drugs, vaccines etc.
What is Bacterial Meningitis?
Common causes?
Pathogenesis?
Diagnosis?
Symptoms include:
- Fever
- Headache
- Meningismus
- Nausea
- Vomiting
- Altered mental status
Common bacteria include:
- Strep. pneumoniae
- Haemophilus influenza type B
- Neisseria meningitidis
Pathogenesis: These organisms have the ability to colonise the nasopharynx epithelium. Evade IgA by using IgA proteases. Crosses mucus in phagocytic vacuoles and enters blood stream (eluding host reponse with their polysaccharide capsule).
Releases endotoxin. Toxin alters coagulation and inflammatory processes leading to rash (Petechial Rash)
Diagnosed by: Selective Culture, gram -ve diplococcic
What is Meningismus?
Stiff neck associated with meningitis.
What are the 4 signs of meningeal irritation?
Hint: They are physical tests done during examination. (Long answer)
- Anterior neck flexion - Pain on flexion = neck stiffness
- Kernig’s Sign - pain in lower back or posterior thigh when patient is supine, hip flexed at 90degrees and patient is asked to extend their knee.
- Brudzinski’s Sign - With patient supine and holding head –> flex their head anteriorly –> positive if patient flexes knees and hip in response to this manoeuvre (random AF)
- Jolt test: Ask patient to move head side to side at frequency of 2-3 rotations per second - positive if it worsens their headache.
What areas should a physical examination target?
- Skin - looking for Petechial Rash of meningiococcemia
- Tympanic membranes - looking for otitis media as a portal of entry for pneumococcal meningitis
- Optic disks - looking for evidence of papilloedma - as a relative contraindication to lumbar puncture. ( Pulsations in central vein effectively exclude increased intracranial pressure - lumbar puncture is fine to do)
What is viral meningitis?
AKA Aseptic meningitis.
- Most common type of meningitis
- Majority of cases caused by Enterovirus
(Single stranded RNA (+ssRNA) that lacks envelopes)
- No specifc treatment - Just rest and fluid.
NOT AS SERIOUS AS BACTERIAL.
What is Encephalitis?
Viral or bacterial infection causing inflammation of the brain. Rare but serious.
- In the UK most common viruses linked are:
- HSV (cold sores and genital herpes)
- Varciela zoster virus (Chickenpox and Shingles)
- -> Rare cases can be fungal or bacterial.
Treatment: Antiviral medication, anticonvulsants, corticosteroids, artificial respiration.
Prevent: Vaccine against virus (?)
EXTRA:
What is Mycosis?
- Cryptococcal meningitis caused by yeast Cryptococcus neoformans
- Can be fatal to immunocompromised patients.
EXTRA:
What is Leprosy
Caused by Myobacterium leporae - aerobic gram +ve acid fast bacteria.
- Only human bacterial pathogen of PNS
- Spreads Person-Person
- Depending on immune response it can be either:
1. Tuberculoid (non progressive) OR
2. Lepramatous (progressive) - loss of facial features etc.
Secondary infections of lepron lesions may be fatal.
EXTRA
What is Rabies?
Zoonotic disease caused by Rabies virus (-ssRNA)
- results in degenerative brain and spinal cord disease
Symptoms:
- Pain
- Itching (at site)
- Fever
- Headache
- Malaise
Pathogenesis:
Virus attaches and triggers endocytosis into skeletal muscle - once inside the virus replicates
The virus then uses neuromuscular junctions to enter neurones and the CNS.
Diagnosis: Test for antibodies.
EXTRA
What is Prion Disease?
Fatal neurodegenerative disease caused by proteinacious infective particles.
- subviral in size
- Resistant to inactivation
- PrPc is expressed in a variety of cells including neurones of the CNS –> Where it may act as a copper binding protein –> thought to play a role in synaptic function.
During prion infection, PrPc appears to undergo conformational change to convert to PrPsc
EXTRA
What is Cruezfeldt-Jacob disease?
Characterised by a range of neuropathies including:
Spongiform changes, neuronal loss, Astrocytosis, accumulation of PrPsc, Amyloid plaque formation.
Main subgroups of CJD:
- Idiopathic
Cause unknown (Sporadic CJD - 90% of case)
- usually presents as rapidly progressing dementia of less than 1 year in duration
- Naturally occurring polymorphism at codon 129 in prion protein gene (Major influencing factor in determining susceptibility to sporadic CJD) - Familial CJD
- Occuring as autosomal dominant (Familial CJD 10% of cases)
- -> associated with mutations or insertions in the ORF of the human prion protein gene on chromosome 20 - Acquired Disorders following Accidental Infection by Inoculation or Ingestion
- CJD not a communicable disease but some transmission is possible (Transplant contaminated, surgical instruments, ijection of Growth Hormone from infected pituitary gland.
EXTRA
What is African Trypanosomiasis
African Sleeping Sickness
Caused by Trypanosoma brucei gambiense
- A protozoa transmitted by the Tsetse fly
Three stages of disease;
1. A lesion formed at site of bite with dead cells & parasites
- Parasite in blood causes;
- Headache
- Fever
- Swelling of lymph node
In early stage the protozoa is found in low numbers in the blood (2-4 years) - When parasite invades the CNS, encephalitis resulting in neurological complications & extreme drowsiness.
- sufferer becomes so tired they can no longer eat. Slip into coma & die.
–> currently no vaccine - as the parasite changes glycoprotein antigen when it replicates.
Host struggle to mount an immune defence.
Suramin can be used in early stage of disease - but arsenic based drug is used when parasite is in the brain.
