Pathophysiology
1) cause is exotoxin (tetanospasmin) from Clostridia tetani 2) spores contaminate devitalized tissue (wounds, umbilical remnant) and germinate into bacteria 3) toxin is released and travels to CNS by retrograde axonal transport when bacteria lyse 4) toxin prevents release of an inhibitor on postsynaptic spinal neuron
Signs and Symptoms
1) increased muscle tone and spasms 2) seizures 3) weakness and paralysis in late stages 4) abrupt tonic contraction of voluntary muscles first in injury area and then in the jaw 5) pain/stiffness in neck and shoulder 6) arched back (opisthotonos) 7) facial sneer (risus sardonicus) 8) autonomic impairment (hypotension, sweating, tachycardia) 9) respiratory failur is usual cause of death
Characteristic Test Findings
Laboratory – 1) increased WBC count 2) normal lumbar puncture
Histology/Gross Pathology
1) large anaerobic, spore-forming, gram-positive rods 2) spore is terminal giving the organism a “tennis racket” or “drumstick” appearance
Associated Conditions
germination of spore and subsequent toxin release is enhanced by presence of – calcium salts, necrotic tissue, concurrent pyogenic infection
Biochemistry
1) C. tetani germinates only in wounds with low oxidation-reduction potential 2) toxin blocks release of inhibitory glycine and GABA from neurons and Renshaw’s cells in spinal cord
Inheritance/Epidemiology
1) incubation period is 4-5 days 2) mortality rate of generalized tetanus is 50% 3) disease of children in poor countries 4) occurs worldwide in soil and animal feces 5) in USA most cases follow acute, penetrating injury
Treatment
1) prevention is easier than cure 2) immunization with toxoid 3) if previously immuninzed a booster shot of toxoid is given 4) booster shot and the antitoxin given at different sites on the body 5) after symptoms present – sedation, mechanical ventilation if needed, muscle relaxants like diazepam, surgical debridement of injury site, and metronidazole or penicillin (somewhat controversial)
Tips for USMLE
1) tetanus toxoid is tetanus toxin neutralized with formalin 2) increased tone in masseter muscles (trismus, lockjaw) is first presentation 3) taut central muscles occur (neck, shoulders, back, and abdomen) but hands and feet are relatively spared
Thank for info.