Polymyalgia rheumatica

Definitions & Key takeaways

Polymyalgia rheumatica (PMR) is an autoimmune disorder that causes inflammation in the muscles and joints, resulting in joint pain and stiffness, usually in the shoulders and hips. Symptoms usually develop in people over the age of 50 and may include fatigue, muscle and joint pain, stiffness, loss of appetite, weight loss, and fever. Treatment of polymyalgia rheumatica focuses on suppressing the immune response, usually with low doses of corticosteroids, such as prednisone. Specific exercises and a healthy diet can also help strengthen the muscles and bones, as well as improve flexibility of the affected joints.

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Introduction0:00–0:39

With polymyalgia rheumatica, “poly-“ means many, “mya-” means muscles, and “-algia” means pain. “Rheumatica” comes from rheumatism, which broadly refers to conditions that affects the joints and connective tissue.
So, polymyalgia rheumatica is a disorder that causes muscle pain and joint stiffness. It is considered to be an immune- mediated disease, meaning that the immune system attacks our own body.
It is important to note that although “myalgia” means muscle pain, the muscles are usually spared and it’s the tissue around the joints that mostly gets inflamed.

Physiology0:39–2:11

Normally, the cells of the immune system are always hanging around, ready and excited to spot and fight against anything foreign that could cause harm inside the body.
One particular type of immune cell - the dendritic cell - is a type of antigen-presenting cell, meaning that it grabs a pathogen for example a bacteria, destroys it, and presents a part of that bacteria, called an antigen, to other immune cells.
Dendritic cells take their name from the fact that they have branch like arms called dendrites which help them grab antigen.
Dendritic cells take their captured antigen and move over to a nearby lymph node, where they present the antigen to a helper T-cell.
Dendritic cells “present” the antigen on a protein called a major histocompatibility complex, or MHC, class II molecule which is on their cell surface.
MHC class II molecules are like a serving platter, which hold the antigen as it gets presented to the helper T-cells. Once these antigens are recognized as foreign, T-helper cells get activated and start secreting a lot of proinflammatory cytokines, or signalling molecules, that recruit more immune cells, such as macrophages, to the site of inflammation.
At the same time, other cytokines, called interleukins, trigger B-cells to secrete antibodies against the targeted antigens.
These antibodies block pathogens from causing harm, and also “tag” them so that other immune cells, like macrophages, can recognize and destroy them.

Causes2:11–3:06

Although the exact cause of polymyalgia rheumatica is not well understood, it is associated with both genetic and the environmental factors.
For example, a person with a certain gene for an MHC class II molecule, also called a human leukocyte antigen, or HLA–DR4, is more likely to develop the disease especially after an infection with adenovirus or parvovirus B19.
This may be due to a process called molecular mimicry, which is where an immune cell mistakes a protein in the body for being a foreign protein.
When our own proteins trigger an immune response, the protein is called an autoantigen. So, these autoantigens get picked up by antigen-presenting cells, which go on to activate helper T-cells.
These helper T-cells, in turn, activate B-cells which start producing antibodies against the autoantigens. Then, both helper T-cells and antibodies enter the circulation and reach the large joints, such as the shoulder and hip.

Pathology3:06–4:23

Once there, they secrete cytokines like interferon-γ to recruit more immune cells like macrophages. Macrophages head over to those joints and produce inflammatory cytokines, like tumor necrosis factor alpha, or TNF-α, interleukin-1, and interleukin-6 which together with the T-cell’s cytokines, promote inflammation of the joint lining.
Now, although it’s called polymyalgia, the muscles themselves are not inflamed and actually appear normal on biopsy. Instead, the pain comes from the structures surrounding the joints like the tendons and bursae, rather than the joints themselves, and that affects nearby nerves in the muscle, called referred pain.
Meanwhile, these inflammatory cytokines travel through the bloodstream and reach other organs. For example, interleukin-1 and interleukin-6 travel to the brain, where they act as pyrogens, inducing fever.
In fact, polymyalgia rheumatica is also strongly associated with giant-cell arteritis. That’s a condition where there’s inflammation of the walls of the arteries in the temples, which is why it’s also called temporal arteritis.
Polymyalgia rheumatica often affects women over 50 years of age, and typically causes symptoms like pain and stiffness of the shoulder and hip, which often starts on one-side, but typically progresses to both sides within weeks.

Symptoms4:23–5:08

The symptoms are usually more severe in the morning and at night, often lasting for more than an hour, and they typically improve after activity.
The pain can make it hard to get out of bed or up from a chair, and lifting the arms above shoulder height can be tough.
It can also cause a low grade fever, fatigue, and loss of appetite which can lead to weight loss. Also, many people can develop temporal arteritis which causes symptoms like severe headache, jaw pain, and vision problems - and even blindness.

Diagnosis5:08–5:35

The diagnosis of polymyalgia rheumatica can be confirmed by increased inflammatory markers, like a high erythrocyte sedimentation rate, or ESR, and C-reactive protein, or CRP.
Since there is little damage to the muscles, muscle enzymes like creatine kinase, usually remain normal, which distinguishes polymyalgia rheumatica from other inflammatory muscle disorders, like polymyositis.

Treatment5:35–5:55

Treatment of polymyalgia rheumatica focuses on suppressing the immune response, usually with low doses of corticosteroids, such as prednisone.
Specific exercises and a healthy diet can also help strengthen the muscles and bones, as well as improve flexibility of affected joints.
All right, as a quick recap, polymyalgia rheumatica is an inflammatory disorder that causes pain or stiffness, usually in the shoulders and hips, and is commonly associated with temporal arteritis.

Review5:55–6:23

There’s usually an elevation in inflammatory markers, but the creatine kinase is usually normal, which distinguishes it from other inflammatory muscle disorders, like polymyositis.