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Sarcoidosis

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Sarcoidosis

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Sarcoidosis

17 flashcards
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USMLE® Step 1 style questions USMLE

5 questions
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A 55-year-old African-American man presents to his primary care physician with shortness of breath and fatigue over the past several months. He complains of diffuse pain in his joints as well as a rash that appeared over his lower extremities. He reports “I’m just not feeling like myself, and I’m starting to wonder if I’m depressed.” His past medical history is notable for obesity, hypertension, and a 20-pack-year smoking history. He works as a construction contractor. Temperature 37°C (98.6°F), pulse is 62/min, respirations are 14/min, and blood pressure is 147/94 mmHg. BMI is 33 kg/m2. Physical examination is notable for submandibular and axillary lymphadenopathy, as well as red tender lumps on the anterior shins. He subsequently undergoes lymph node biopsy that demonstrates the following pathologic lesion:  

 
Reproduced from: Wikipedia    

Which of the following laboratory findings is most commonly associated with this clinical condition?  

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Transcript

Contributors:

Sam Gillespie, BSc

With sarcoidosis, sarcoid refers to the flesh and osis means disorder - and the reason that it’s called that, is that sarcoidosis is an immunologic disorder that results in lots of small nodules forming throughout the body.

The disease is poorly understood and is most common among African American females.

Normally, the cells of the immune system are ready to spot and destroy anything foreign pathogens that could cause the body harm.

To help with this, there’s a category of cells in the body called antigen-presenting cells, which include macrophages, B-cells, and dendritic cells.

The most common antigen presenting cells are the dendritic cells which are named after their branch like arms called dendrites.

When an dendritic cell comes in contact with a pathogen, it latches onto it with its dendrites and then engulfs or swallows it.

The pathogen is broken down and the cell presents a piece of it, called an antigen, on a major histocompatibility complex class II molecule, or MHC-class II for short.

Then the dendritic cell carries the antigen to the lymph node to find some naive helper T-cells which are T-cells that have never seen an antigen before.

Eventually it runs into a naive helper T-cell with a T-cell receptor that recognizes and binds to the antigen.

Cytokines are then released by dendritic cell to help activate the helper T-cell and it begins to divide or proliferate.

The new T-cells leave the lymph node and start secreting proinflammatory cytokines, or signaling molecules, that recruit more immune cells like additional T-cells and macrophages.

In sarcoidosis, this process unfolds over and over throughout the body without the presence of a specific pathogen that the body is trying to destroy.

In other words, the immune system seems to be going a bit haywire in the absence of a pathogen.

The precise trigger isn’t known, but there are some known genetic and environmental risk factors.

Genetic risk factors include being African American and having a family member with sarcoidosis.

Environmental risk factors include a prior infection with Mycobacterium tuberculosis and Borrelia burgdorferi, but to be specific, these pathogens are long gone when the autoimmune problem sets in.

So when sarcoidosis is triggered, T cells and macrophages get attracted to a particular spot of healthy tissue.

Sarcoidosis can involve nearly every organ, but they most often involves hilar lymph nodes which are lymph nodes that are near the point where the bronchi meets the lung.

As more and more immune cells gather at a particular spot, they form small nodules called granulomas with T cells on the periphery and macrophages in the center.

The granulomas in sarcoidosis are noncaseating which means that there is no tissue necrosis at the center of the granuloma, unlike some other granulomatous diseases like tuberculosis.

Oftentimes, macrophages fuse together to form a single large multinucleated cell called a Langhans giant cells.

Summary
Sarcoidosis, also called sarcoid, is a disease involving abnormal collections of inflammatory cells (granulomas) forming as nodules in multiple organs. Although any organ can be affected, such nodules usually appear in the lungs or its associated lymph nodes. Sarcoidosis seems to be caused by an immune reaction continuing after the initial infection or causative antigen is cleared from the body. Sarcoidosis usually resolves without any medical intervention, but some cases become chronic or develop life-threatening complications.
Sources
  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Sarcoidosis" Orphanet Journal of Rare Diseases (2007)
  6. "Human Leukocyte Antigen Class I Alleles and the Disease Course in Sarcoidosis Patients" American Journal of Respiratory and Critical Care Medicine (2004)
  7. "Pathogenesis of sarcoidosis" La Presse Médicale (2012)
  8. "Corticosteroids for pulmonary sarcoidosis" Cochrane Database of Systematic Reviews (2005)