USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 19-year-old man comes to the emergency room because of difficulty breathing for 6 hours. He reports that earlier that day, he was doing laundry and suddenly became short of breath. He also reports back pain for a year that is worst after waking up in the morning. He reports that his morning stiffness typically lasts for approximately an hour. Over the past few months, he has noticed pain in his hips intermittently but did not have insurance to see a doctor so he ignored it. Chest and spine X-rays are obtained. Which of the following is associated with the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
So ankylosing spondylitis is a chronic inflammatory disease that affects the vertebral joints and makes the spine really stiff, but can also cause inflammation in other parts of the body like the eyes and blood vessels.
Ankylosing spondylitis, also called Bechterew disease, is part of a group of diseases called seronegative spondyloarthropathies.
Spondyloarthropathies are all autoimmune diseases that affect the joints, and they’re seronegative, which refers to the fact that rheumatoid factor, which is an autoantibody, is not found in the blood.
Alright, so in the healthy adult, the vertebral column is made up of 33 bones.
Below the sacrum is a tiny bone called the coccyx or tailbone.
There are two types of joints between the vertebra.
Between each of the vertebral bodies is an intervertebral disc which is made of type I and type II collagen and has two parts, the annulus fibrosis, an outer fibrous ring, and the nucleus pulposus, an inner jelly-like substance.
This disc forms a joint between each vertebra, and it allows slight movement and acts as a shock absorber.
These joints are synovial, meaning they have a joint capsule and a small amount of synovial fluid in between.
When you stretch your back the capsule in these joints stretches too and decreases the pressure in the joint space, which makes any gas suddenly come out of solution, making a cracking sound!
They help guide and limit the range of motion in your spine.
In ankylosing spondylitis there’s chronic inflammation of the intervertebral joints and the facet joints of the spine.
The exact cause of the inflammation is unclear, but it’s thought to be due to an autoimmune process - which is when the immune system attacks its own tissue - in this case the type I and type II collagen in the joints.
But unlike many other autoimmune conditions, no autoantibody has been specifically linked to the disease.
Normally, the cells of the immune system are ready to spot and destroy anything foreign that could cause the body harm.
To help with this, most cells in the body have a set of proteins that combine together to form something called a major histocompatibility complex, or MHC, class I molecule that sits on the surface of their cell membrane.
Most individuals with ankylosing spondylitis have the gene HLA-B27, which is a gene that encodes for a specific type of MHC class I molecule.
These surface proteins act kind of like a serving platter, presenting molecules from within the cell for the immune system to continually sample.
Normally though the molecule’s just a sample from the cell, and the immune system recognizes it as harmless, and this is known as a self-antigen, and there’s no response.
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