Pathophysiology
1) cause is infection with Corynebacterium diphtheriae 2) only known host is human 3) organism grows and colonizes on mucous membranes 4) clinical syndrome is caused by absorption of diphtheria toxin by mucous membranes and then systemic spread
Signs and Symptoms
1) sore throat and unwillingess to eat 2) fever 3) malaise 4) enlarged cervical lymph nodes 5) grayish membranes on tonsils causing respiratory obstruction 6) neck edema 7) weakness 8) headache 9) hoarseness 10) cough 11) systemic effects of pallor, listlessness, and hypotension 12) skin lesions are often ulcerated and necrotic
Characteristic Test Findings
Laboratory – definitive diagnosis is by isolation of the organism, which requires tellurite medium to grown
Histology/Gross Pathology
1) gram-positive rod in the classic “Chinese letter” shape 2) necrosis in cardiac, hepatic, renal, and adrenal tissue 3) two main strains are tox+ (causes respiratory symptoms) and tox- (causes skin lesions)
Associated Conditions
1) myocarditis 2) polyneuritis 3) arthritis 4) pneumonia 5) renal failure 6) encephalitis
Biochemistry
diphtheria toxin is produced only in low-iron environments (human body)
Inheritance/Epidemiology
1) transmission is via aerosolization, skin wounds, or abrasions 2) incubation period is 1-6 days 3) usually a disease of small children 4) largely eliminated in developed countries via vaccine 5) gene for the toxin is carried on a bacteriophage (beta-corynephage)
Treatment
1) prophylaxis is via the DPT gene or more current DTaP vaccine of childhood 2) after infection, antitoxin is given (10% have serum sickness as antitoxin is produced in horses 3) erythromycin or procaine penicillin is used to eradicate the organism in carriers and prevent spread 4) cutaneous lesions are debrided of necrotic tissue and then wiped with Burow’s solution 5) prophylactic tracheostomy if loss of airway is impending
Tips for USMLE
1) the standard antibiotics are not effective against the acute diphtheria lesion and antitoxin must be given to resolve acute condition 2) if the question mentions “bull-neck” edema, think diphtheria
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