Page 1 of 2: q.microbiology!

sravya · Credits: 28740 My Scrapbook

A 4-year-old boy presents to the emergency room with muscle spasms. His past medical history is significant for
recurrent infections and neonatal seizures. Evaluation of his serum electrolytes reveals hypocalcemia. This
patient would be most susceptible to which of the following diseases?

A. Chickenpox

B. Diphtheria

C. Gas gangrene

D. Gonorrhea

E. Tetanus

sal · Credits: 23054 My Scrapbook

E. Tetanus

georgie · Credits: 8465 My Scrapbook

its digeorge syndrome so his cell mediated immunity is gone

but it makes him susceptible to all diseases??

? gas gangrene?

ratnakar_potla · Credits: 5713 My Scrapbook My Reading List 2 Books

i am not sure abt digorge but it is a common presentation for neonatal tetanus.............. even if its digeorge........then all should be the answer and its not possible so it should be tetanus

draashna · Credits: 907 My Scrapbook

I think it should be A. As defective cellmediated immunity in digeorge's syndrome predisposes to viral,fungal n protozoal infections..
corect me if i m wrong...

drche · Credits: 11979 My Scrapbook My Reading List 10 Books

shud be tetanus...
cudos,che..

manpreet108 · Credits: 30702 My Scrapbook

i think diphtheria.

this is digeorgies syndrome.
that wd increase the susceptibility to all infectns-viral,fungal,bacterial--but going with age of this child-4 yrs --even in normal child diphtheria peaks in this age group --so in this child susceptibility wd be even more increased..

thats my opinion.....comments welcome.

dana · Credits: 3703 My Scrapbook My Reading List 9 Books

a.chicken pox.

sravya · Credits: 28740 My Scrapbook

The correct answer is A. This boy has DiGeorge's syndrome, as evidenced by his tetany (muscle spasms) due
to hypocalcemia and his history of recurrent infections and neonatal seizures. The syndrome occurs because
of an embryonic failure in the development of the third and fourth pharyngeal pouches. Patients have both
hypoplastic parathyroids (producing hypocalcemia) and thymuses (producing T-cell deficiency and recurrent
infections). Since cell-mediated immunity (which depends on T cells) is important in defense against infections
caused by intracellular pathogens (such as viruses), patients with DiGeorge's are particularly susceptible to
viral infections, such as chickenpox (varicella). They also have trouble with fungal pathogens (e.g., Candida)
and mycobacteria.

HEY Note that the USMLE might ask you other questions about DiGeorge's syndrome(coz its one of the high yield topic i have seen atleast one qs in Microbiology in every book i referred), so you should be able to
recognize other clues to the diagnosis, including: congenital cardiac defects, esophageal atresia, bifid uvula,
short philtrum, hypertelorism, antimongoloid palpebral slant, mandibular hypoplasia, and low-set ears.

Diphtheria (choice B) is caused by Corynebacterium diphtheriae, which produces disease by the elaboration
of a very potent exotoxin. Therefore, humoral immunity (antitoxin), which is not usually compromised in
DiGeorge's patients, is essential for defense against the organism. (Note that the C. diphtheriae exotoxin acts
by causing the ADP-ribosylation of elongation factor-2 of eukaryotic cells, thereby inhibiting protein synthesis).
The disease can be avoided by immunization with diphtheria toxoid.

Gas gangrene (choice C) is caused by Clostridium perfringens, which produces a potent alpha toxin that
injures cell membranes. Therefore, humoral immunity would again play a predominant role in defense against
this organism. Note that the disease occurs in wounds and would not be expected in an uninjured 4-year-old
boy.

Gonorrhea (choice D) is caused by Neisseria gonorrhoeae and would not be expected in a 4-year-old boy
unless there was evidence of sexual abuse. Virulence factors of this organism include pili, cell wall endotoxin
and outer membrane, and secretory IgA protease. Antibody responses, neutrophils, and complement are of
prime importance in defense against gonococcal infections.

Tetanus (choice E) is caused by Clostridium tetani and serves as a tricky distracter, as you might have quickly
associated the patient's muscle spasms with this answer choice. (This is why it is important to read the
question stem carefully before prematurely jumping to the responses). C. tetani, which gains entry through
deep wounds, produces tetanus toxin (exotoxin) and can be prevented by immunization with tetanus toxoid.

sal · Credits: 23054 My Scrapbook

Hi sravya

Excellent question and fantastic explanations.

Thanks

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