THE USMLE TIMES - #80
Highlights for the week of June 17, 2024
Welcome to issue #80 of The USMLE Times… We’ve now posted a USMLE-specific newsletter eighty weeks in a row! Welcome to all new members of the community 👋
Here’s what’s on tap for issue #80 of the USMLE Times:
Question of the Week (Histology)
This week’s video training (Get Unstuck From Average)
Tweet thread of the week
Links to recent training
Question deep-dive & breakdown
Let’s dive in!
A group of medical students studying for their histology final are discussing the unique features of rhabdomyosarcomas. If they want to identify the muscle cells of this tumor at the microscopic level, which of the following immunohistochemical markers would be most useful?
A) Cytokeratin
B) Vimentin
C) Mesothelin
D) Chromogranin A
E) Desmin
F) S-100
G) GFAP
The answer & question breakdown is at the bottom of the post.
📺 USMLE TRAINING 👇
💬 TWITTER THREAD OF THE WEEK
READ THE FULL THREAD HERE.
Click HERE To Follow Us On Twitter/X
🔗 LINKS TO RECENT POSTS
Should I Take Step 3 Before Match? - READ HERE
USMLE Times Issue #79 - READ HERE
Suffering From Premature P.O.E.? - READ HERE
USMLE Times Issue #78 - CLICK HERE
The USMLE Success Limiting Skillset - READ HERE
USMLE Times Issue #77 - CLICK HERE
The Hidden Danger of Mixed Questions - READ HERE
MYSTERY DIAGNOSIS OF THE WEEK
Last week’s answer: Erdheim-Chester Disease (details)
ANSWER + QUESTION BREAKDOWN
The Mental Model for this week’s question:
Step 1. Identify the goal of the question (ID the correct tissue being targeted).
Step 2. Name the correct immunohistochemical marker.
Step 3. Look down to find the correct answer.
GENERAL ANALYSIS
The question asks which immunohistochemical marker would be most useful for identifying muscle cells in rhabdomyosarcoma. Rhabdomyosarcoma is a malignant tumor of skeletal muscle origin, and identifying it accurately requires specific markers that highlight its muscle cell characteristics. The correct marker should be specific to muscle cells.
ANSWER CHOICES:
ANSWER CHOICE A: CYTOKERATIN
Cytokeratin is a marker for epithelial cells and is commonly used to identify carcinomas.
ANSWER CHOICE B: VIMENTIN
Vimentin is a marker for mesenchymal cells and is expressed in various sarcomas.
ANSWER CHOICE C: MESOTHELIN
Mesothelin is a marker often used to identify mesotheliomas and other types of cancers.
ANSWER CHOICE D: CHROMOGRANIN A
Chromogranin A is a marker for neuroendocrine cells and is used to identify neuroendocrine tumors.
ANSWER CHOICE E: DESMIN
Desmin is an intermediate filament protein found in muscle cells and is a specific marker for muscle differentiation.
ANSWER CHOICE F: S-100
S-100 is a marker to identify neural crest-derived cells, such as melanocytes and Schwann cells.
ANSWER CHOICE G: GFAP (Glial fibrillary acidic protein)
GFAP is a marker for glial cells and is used to identify glial tumors.
FINAL VERDICT…
Desmin is an intermediate filament protein that is specifically expressed in muscle cells, including skeletal, cardiac, and smooth muscle. In the context of rhabdomyosarcoma, desmin is a crucial immunohistochemical marker because it confirms the muscle origin of the tumor cells. Desmin staining is positive in almost all cases of rhabdomyosarcoma, making it a reliable marker for identifying muscle differentiation in these tumors. This specificity is essential for distinguishing rhabdomyosarcoma from other small round blue cell tumors that may appear similar under the microscope but do not originate from muscle tissue.
FINAL ANSWER: E: DESMIN
That’s it for issue #80 of The USMLE Times!
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