L06: Musculoskeletal/Nervous System (Brown) Flashcards
Bone sites predisposed to infection
- site of traumatic injury
- areas of active growth with increased vascularity
- sites with special vascular features (ie. Discontinuous epithelium in capillaries in vertebral end plates and metaphyses)
Primary cause of diskospondylitis
Hematogenous spread of systemic infection
Primary cause of vertebral osteomyelitis
Penetrating wound
Osteomyelitis
Inflammation of the medullar cavity of a bone
-can be caused by hematogenous spread or post-trauma
Bone infections assoc. with intervertebral disk infections
- osteitis
- osteomyelitis
- periostitis
Bacterial agents assoc. with arthritis
Strep Borrelia burgdorferi Staph pseudintermedius Mycoplasma felis Mycoplasma spumans
Bacterial agents assoc. with diskospondylitis
- actinomyces sp.
- Strep
- Brucella canis
- Staph pseud.
Bacterial agents assoc. with myositis
- strep (dog)
- obligate anaerobes
- Pasteurella multocida (cat)
- staph pseud.
Bacterial agent(s) assoc. with necrotizing fasciitis
Beta-hemolytic strep (dog)
Bacterial agent(s) assoc. with osteomyelitis
Actinomyces
Brucella canis
Staph pseudintermedius
Bacterial agent(s) assoc. with polymyositis
Leptospira sp.
Most common cause of bacterial bone infection
Staphylococcal species (46-74%), usually staph pseudintermedius
Others:
-strep, gram - aerobes, anaerobes
Common clinical features with anaerobic osteomyelitis
- follows fractures, trauma, or bite wounds
- putrid exudate or gas in soft tissues
- “sterile” cultures despite signs of infection
- multiple microorganisms in gram-stained specimens
Agents of mycotic bone infections
(Usually via hematogenous spread)
- cryptococcus neoformans
- coccidioides immitis
- Aspergillus species
- Penicillium species
- Blastomyces dermatitidis
- Histoplasma capsulatum
T/F: synovial fluid aspirate often negative in septic joint
T
Abx for septic joints
- based on C/S
- penicillins, cephalosporins, and aminoglycosides penetrate bone well
- clindamycin penetrates bone and works well against grampos and anaerobic osteomyelitis
Fluroquinolones in tx of bone/joint infection
- good bone penetration
- not effective against gramnegs and mycoplasma under anaerobic conditions
- avoid in immature animals - bad for growing cartilage
Components of central nervous system
Brain
Spinal cord
CSF
Meninges
Components of peripheral nervous system
- Cranial and spinal nerves that innervate muscles/effector organs
- somatic sensory and autonomic divisions
Nervous system infections most commonly involve CNS or PNS?
CNS
Normal flora of nervous system
NONE!
Can have latent infections of herpesvirus and distemper virus
Natural anatomic antimicrobial defense mechanisms in nervous system
- brain, spinal cord
- meningeal layers
- BBB (capillary endothelial cell tight junctions)
- blood cerebrospinal barrier (protects pituitary and choroid plexus)
- blood nerve barrier (protects PNS nerves from inflammatory rxns)
Nervous system immune defenses
- MHC expressed by astrocytes and microglial cells in CNS parenchyma
- major function = immunosurveillance, NOT response
Innate defenses of nervous system
- Complement (recruits leukocytes, kills via membrane attack complex)
- Microglia cells (act as macs)
- Dendritic cells
- Astrocytes (produce cytokine)
- Nerve cells (produce IFN)
Chars. Of infections of the nervous system
- most involve brain or meninges
- other sites may be co-involved or act as targeted site
- spinal cord involvement rare due to dec. blood flow
- microbial toxins can act even if pathogen not present
- injury from direct cytotoxic effects, inflammatory response, or both
Routes of infection to nervous system
- hematogenous most common
- retrograde movement within neurons
- extension of infectious process from contiguous sites
- secondary to FB near head or spine
- iatrogenic infection (ie. Contaminated spinal needles)
- CSF if patient with bacteremia
Mechanism of CNS injury
- vascular damage (usually due to septicemia and bacterial embolization of the CNS)
- brain parenchyma or meninges (inflammatory response, myelin formation)
CS of meninges lesion
Back rigidity, depressed mental state
CS of cerebrum lesion
Circling, behavioral changes, seizures
CS of brainstem lesion
Cranial nerve deficits, head tilt
CS of cerebellum lesion
Ataxia, tremors
CS of spinal cord lesion
Tetraplegia
Chars. Of meningoencephalitis
- meningitis + encephalitis
- CS of meningitis usually precede CS of encephalitis
CS of meningitis
- fever
- hyperesthesia
- neck rigidity
- painful paraspinal muscle spasms
+/- depression, blindness, paresis, ataxia, opisthotonos, CN deficits, seizures, dementia, agitation, depressed consciousness
Most reliable and accurate means of identifying meningitis or meningoencephalitis
Analysis of CSF
Rabies causes what CNS CS?
Aggressive behavior, paralysis
Pseudorabies virus causes what CNS CS in dogs?
Intense pruritus
Seizures
Pseudorabies virus causes what CNS CS in cats?
Hyperexcitability
Paralysis
Paresis
CNS CS of cryptococcus neoformans
Dogs: ataxia, head tilt, paresis, seizures
Cats: ataxia, paresis, CN deficits, seizures
*often the inflammation, not the pathogen itself causes the problems
Canine viruses that cause nervous system CS
Adenovirus 1 (seizures)
Distemper (seizures, ataxia)
Herpesvirus (seizures, depression, back m. Spasm)
Feline viruses that cause nervous system CS
Panleukopenia (ataxia)
FIV (aggressive or psychotic behavior, seizures)
FIP (ataxia, paresis, seizures)
FeLeuk (abn. Vocalization, hyperesthesia, paresis)
Canine bacterial infections that cause CNS CS
Otitis (E. Coli, proteus, pseudomonas, staph, strep) –> vestibular dysfx
Ehrlichia canis: ataxia, cerebellar/vestibular dysfx, seizures
Clostridium botulinum –> flaccid paralysis, paresis
Clostridium tetani –> back m. Spasm, seizures, tremors
Rickettsia rickettsii –> ataxia, depression, vestibular dysfx, seizures
Treatment of nervous system infection
Little benefit except for animals w/ probably immune-mediated, steroid-responsive inflammatory CNS diseases, or animals w/ meningoencephalitis caused by rickettsia and certain bacteria
-higher dosages of abx may be needed to maintain adequate conc. In the CNS
What type of abx rec. for tx of CNS infection?**
BACTERICIDAL (not static)
Ampicillin, metronidazole, tetracyclines, TMS, fluoroquinolones, 3rd gen. Cephalosporins
Natural defenses of MS system
- circulatory immune system
- constant bone remodeling
