Thread by @MayoClinicINFD

Images of Infectious Diseases

This is the histopath and gram stain of culture of a lymph node biopsy of a person with tender purulent inguinal adenopathy.
Dr. @dwchallener
Dr. @ali_eberly
MCQ #MayoIDQ to follow

72M. Crohn’s. 2 pet dogs. 1 pet cat.
2 mo after L knee surgery —> tender L inguinal node with purulence. No F/C. No response to TMP-SMX.

Biopsy (see photo): Stellate suppurative granuloma with central necrosis and clumps of bacteria.

What is the most likely diagnosis?

1/
#Gram stain: a first step in bacterial identification —> two major groups:
1. Gram-positive: retains primary stain (crystal violet)
2. Gram-negative: does not retain crystal violet but counterstained by safranin/fuchsine —> red / pink

Named after Hans Christian Gram (photo)

2/
#Gram stain and morphology classifies bacteria into:
Gram (+) coccus / bacillus
Gram (-) coccus / bacillus

Gram stain of our case (photo) shows clumps of purple rods —> Gram (+) bacillus (photo)

3/
As suggested by @Dr_Jeremy_Young , this mnemonic “ABCDE LT” is used to easily remember Gram + bacillus

Actinomyces group (incl. Nocardia)
Bacillus
Clostridium
Diphtheroids (corynebacterium)
Erysipelothrix

Listeria / Lactobacillus
T. whipplei

4/
#Bartonella henselae was picked by 49% of responders

#CatScratchDisease is a top DDx in patient with febrile lymphadenitis + cat exposure!!!

However....
Bartonella henselae is NOT a gram+ bacillus (it is Gram-negative bacillus)

5/
#Bartonella henselae #CatScratchDisease

1. Scratch/bite of cat; cat fleas
2. Hallmark: Lymphadenitis
3. Spread visceral organs: FUO in children (necrotizing granuloma in liver / spleen)
4. Dx: serology; culture (GNR); PCR; Warthin-Starry stain
5. Rx: azithromycin. TMP-SMX.

6/
#Yersinia pestis causes #lymphadenitis
1. Zoonotic; fleas (rodent fleas, scratch of cats, animals, lab exposure)
2. #Bubonic plague
3. Others: pneumonic, septicemic
4. Dx: culture; GNR with “closed safety pin” bipolar staining
5. Rx: streptomycin; AG; alt: doxy / tetra / FQ

7/
Case diagnosis: #Corynebacterium ulcerans

As per @ncabrera and @jabarcag , the Gram stain morphology is suggestive of corynebacterium (“snapping” division —> clusters and palisade arrangement that mimics “Chinese letters”)

#Clostridiodes difficile does not cause #buboes

8/
#corynebacterium ulcerans

Zoonotic (dogs, cats, other animals) but rarely cause human illness

Closely related to C. diphtheria and C. pseudotuberculosis

May produce toxin and cause a diphtheria-like respiratory / cutaneous illness

academic.oup.com/cid/article/46…

9/
One tweet on #diphtheriae

1. Toxin
2. Carrier, cutaneous, pharyngitis - cervical lymphadenopathy —> toxin absorption: myocarditis, systemic toxicity
3. Hallmark: pseudomembrane
4. Rx: antitoxin + antibiotics (PCN, erythromycin)
5. #VaccineWorks; outbreaks in unvaccinated

/10
Back to the case:

It is possible that patient’s pets (dogs and cat) may harbor corynebacterium ulcerans —> contaminate the wound from recent knee surgery —> regional inguinal adenitis. Underlying Crohn’s Rx may have predisposed to severe disease.

Thanks for participating.