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|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles, Infectious Disease
|SubCategory=General Principles, Infectious Disease
|Prompt=A 55 year old homeless man presents with a 6 month history of a slowly growing lesion in his nasal sinus tracts.  Physical exam is notable for poor dentition, a lack of lymphadenopathy and wooden appearance of the nasal lesion with yellow “sulfur” granules. What is the most likely causal organism?
|Prompt=A 35-year-old homeless man presents to his primary care physician for a right facial lesion that has developed slowly over the past six months.  The lesion forms a sinus tract and is pictured below.  On closer inspection, the physician notices yellow "sulfur" granules within the lesion.  Physical exam is otherwise notable for poor dentition, a lack of lymphadenopathy. What is the most likely causal organism?
 
[[File:WBR0056.jpg | 600px]]
|Explanation=The patient in this vignette is suffering from Actinomyces Israelii.  Actinomyces Israelii is a facultative anaerobe, part of the normal oral flora and able to cause disease only when it is free to replicate in an anoxic environment.  Patients have often recently had dental work, poor oral hygiene, periodontal disease, or radiation therapy causing local tissue damage to the oral mucosa, all of which predispose the person to developing actinomycosis.
|Explanation=The patient in this vignette is suffering from Actinomyces Israelii.  Actinomyces Israelii is a facultative anaerobe, part of the normal oral flora and able to cause disease only when it is free to replicate in an anoxic environment.  Patients have often recently had dental work, poor oral hygiene, periodontal disease, or radiation therapy causing local tissue damage to the oral mucosa, all of which predispose the person to developing actinomycosis.


Educational Objective:
'''Educational Objective:'''
References: First Aid 2012 page 159
 
Tags: #Microbiology #Pathophysiology
'''References:'''
|AnswerA=Staphylococcus Aureus
 
|AnswerAExp=Incorrect - Staph Aureus can cause cutaneous infection (eg Impetigo, Cellulitis) but is not associated the deeper infection crossing tissue boundaries seen in this patient.  S Aureus is also not associated with with sulfur granules (not to be confused with the yellow pigment S Aureus can produce).
First Aid 2014 page 134
|AnswerB=Nocardia Asteroides
 
|AnswerBExp=Incorrect - Nocardia is similar to Actinomyces Israelii in that both are gram-positive rods which form branching filaments, but Nocardia is not associated with sulfur granules and typically causes pulmonary infection in immunocompromised patients.
First Aid 2012 page 159
|AnswerC=Bacillus Anthracis
 
|AnswerCExp=Incorrect- While B. Anthracis can cause cutaneous infections the infected area tends to develop acutely and is darkly colored.  Not associated with draining sinus tracts or sulfur granules.
|AnswerA=Staphylococcus aureus
|AnswerD=Actinomyces Israelii
|AnswerAExp='''Incorrect:''' Staphylococcus aureus can cause cutaneous infection (eg Impetigo, Cellulitis) but it is not associated with the deeper infection that crosses tissue boundaries seen in this patient.  S. aureus is also not associated with with sulfur granules (not to be confused with the yellow pigment S. aureus can produce).
|AnswerDExp=Correct - See Explanation
|AnswerB=Nocardia asteroides
|AnswerE=Mycobacterim Leprae
|AnswerBExp='''Incorrect:''' [[Nocardia]] is similar to Actinomyces israelii in that both are gram-positive rods which form branching filaments. However, Nocardia is not associated with sulfur granules and typically causes pulmonary infection in immunocompromised patients.
|AnswerEExp=Incorrect - Mycobacterium Leprae causes leprosy (Hansen’s disease) which this patient does not have.
|AnswerC=Bacillus anthracis
|AnswerCExp='''Incorrect:''' While B. anthracis can cause cutaneous infections, the infected areas tends to develop acutely and are darkly colored.  Anthrax infection is not associated with draining sinus tracts or sulfur granules.
|AnswerD=Actinomyces israelii
|AnswerDExp='''Correct:'''
|AnswerE=Mycobacterim leprae
|AnswerEExp='''Incorrect:''' Mycobacterium leprae causes [[leprosy]] (Hansen’s disease), which this patient does not have.
|RightAnswer=D
|RightAnswer=D
|WBRKeyword=WJG
|WBRKeyword=WJG
|Approved=Yes
|Approved=Yes
}}
}}

Revision as of 04:07, 24 February 2014
Author PageAuthor::William J Gibson
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::General Principles, SubCategory::Infectious Disease
Prompt [[Prompt::A 35-year-old homeless man presents to his primary care physician for a right facial lesion that has developed slowly over the past six months. The lesion forms a sinus tract and is pictured below. On closer inspection, the physician notices yellow "sulfur" granules within the lesion. Physical exam is otherwise notable for poor dentition, a lack of lymphadenopathy. What is the most likely causal organism?

]]

Answer A AnswerA::Staphylococcus aureus
Answer A Explanation [[AnswerAExp::Incorrect: Staphylococcus aureus can cause cutaneous infection (eg Impetigo, Cellulitis) but it is not associated with the deeper infection that crosses tissue boundaries seen in this patient. S. aureus is also not associated with with sulfur granules (not to be confused with the yellow pigment S. aureus can produce).]]
Answer B AnswerB::Nocardia asteroides
Answer B Explanation [[AnswerBExp::Incorrect: Nocardia is similar to Actinomyces israelii in that both are gram-positive rods which form branching filaments. However, Nocardia is not associated with sulfur granules and typically causes pulmonary infection in immunocompromised patients.]]
Answer C AnswerC::Bacillus anthracis
Answer C Explanation AnswerCExp::'''Incorrect:''' While B. anthracis can cause cutaneous infections, the infected areas tends to develop acutely and are darkly colored. Anthrax infection is not associated with draining sinus tracts or sulfur granules.
Answer D AnswerD::Actinomyces israelii
Answer D Explanation AnswerDExp::'''Correct:'''
Answer E AnswerE::Mycobacterim leprae
Answer E Explanation [[AnswerEExp::Incorrect: Mycobacterium leprae causes leprosy (Hansen’s disease), which this patient does not have.]]
Right Answer RightAnswer::D
Explanation [[Explanation::The patient in this vignette is suffering from Actinomyces Israelii. Actinomyces Israelii is a facultative anaerobe, part of the normal oral flora and able to cause disease only when it is free to replicate in an anoxic environment. Patients have often recently had dental work, poor oral hygiene, periodontal disease, or radiation therapy causing local tissue damage to the oral mucosa, all of which predispose the person to developing actinomycosis.

Educational Objective:

References:

First Aid 2014 page 134

First Aid 2012 page 159
Educational Objective:
References: ]]

Approved Approved::Yes
Keyword WBRKeyword::WJG
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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