Introduction

Polymyalgia Rheumatica and Rheumatoid Arthritis are inflammatory diseases that mainly affect the musculoskeletal system to cause symptoms such as pain, discomfort and stiffness. Polymyalgia Rheumatica (abbreviated as PMR) and Rheumatoid Arthritis (abbreviated as RA) are the most common rheumatic diseases in adults. Although PMR and RA are distinct disorders, their symptoms may be difficult to tell apart and are therefore often mistaken for each other in diagnosis.

However, there are key differences in the symptoms of PMR and RA that may assist in achieving a correct diagnosis. As these diseases may considerably affect your health, it is vital to receive an early and accurate diagnosis so that you may receive the appropriate medical treatment. 

This article will arm you with vital information that may help you recognise if you are at risk of or affected by either one of these diseases. Health awareness is fundamental in ensuring that people seek timely medical attention to prevent or alleviate health complications.

Causes and risk factors

The aetiology of PMR and RA is unknown, but both diseases are believed to be due to the immune system going into overdrive. RA in particular is an autoimmune disorder that results from the immune system attacking the body’s healthy tissues.¹ The same is thought to be the case in polymyalgia rheumatica, however, it has not been confirmed definitively.²

Risk factors for developing polymyalgia rheumatica

Listed here are the risk factors for developing polymyalgia rheumatica:³

• Age: The disease is very rare in people under the age of 50 years, with most cases being in people over the age of 70 years
• Gender: The disease mostly affects people assigned female at birth (AFAB)
• Ethnicity: The disease is most common in white people of Northern European descent
• Genetics: The disease may run within families
• Environmental factors may also contribute to the risk of acquiring the condition

Risk factors for developing rheumatoid arthritis

Listed here are the risk factors for developing rheumatoid arthritis:^4,5,6

• Gender: The disease mostly affects individuals AFAB
  • The risk is increased in individuals AFAB who have never given birth
  • Mothers who have breastfed their young have a reduced risk of developing RA
• Genetics: The disease is likely to run within families
• Smoking: Long-term smoking could lead to RA or exacerbate symptoms in sufferers
• Obesity: Excess body weight could increase risks of developing RA and may reduce the effects of treatment in sufferers
• Periodontitis: There could be a link between RA and gum disease
• Respiratory diseases: There could be a link between RA and ailments of the lungs and airways

Clinical manifestation

Symptoms of polymyalgia rheumatica

The symptoms of PMR are typically general and non-unique, mimicking the symptoms of diseases such as RA. PMR is symptomised by pain and stiffness in the neck, shoulders, arms, hips and thighs. The pain is typically worse in the morning and may disappear spontaneously as the day progresses, or with physical activity. Symptoms may also occur after one has been sitting in a resting position for a long while. 

The complete onset of symptoms mostly takes place within a few days or weeks, but it may also be gradual over longer periods. The symptoms of PMR usually persist for at least 45 minutes and may reduce the range of motion. Consequently, morning activities such as getting dressed become that much more difficult. Symptoms that do not affect the musculoskeletal system may also appear in PMR patients. These include fatigue, fever, loss of appetite, weight loss and general malaise.³ 

Symptoms of rheumatoid arthritis

The symptoms of RA may also be non-specific and seem to be due to PMR. RA is usually signalled by pain, stiffness and tenderness in the fingers, wrists, feet and knees. As the disease progresses, swelling and redness may set in at the affected joints. The affected joints may also feel hot or warm when you touch them. The discomfort associated with RA may be worse in the morning or after a prolonged period of inactivity.⁷ Relief from discomfort may set in after 30 minutes or with physical activity. 

RA symptoms may also be non-musculoskeletal. These include fever, fatigue, weight loss and loss of appetite. Unlike PMR, the symptoms of RA may take up to 6 months to become fully blown. Also worth mentioning is that most RA diagnoses are made for patients between the ages of 30 and 60. However, RA may set in after the age of 60 in what is referred to as elderly onset RA (EORA). RA in younger people is referred to as young onset RA (YORA).⁸

Key differences in symptoms for an accurate diagnosis

The symptoms of PMR and RA may prove to be indistinguishable due to their similarities in pathophysiology. However, there are characteristics of these diseases that are not common to both of them. This is especially true for PMR and YORA. On the other hand, EORA is very similar in its clinical manifestations to PMR.⁸ It is therefore difficult to differentiate between PMR and EORA.⁹

• PMR is specifically due to the inflammation of the muscles, tendons and bursae whereas RA is caused by inflammation in the inner lining of the joints, the synovial membrane
• PMR targets the larger joints such as the shoulders and hips, whereas RA mostly affects the smaller joints such as the fingers, wrists and feet
• PMR usually attacks a joint on one side of the body before attacking the same joint on the other side of the body, whereas RA affects the joints in a symmetric manner
• The symptoms of PMR are typically sudden whereas RA symptoms are more gradual in development
• RA is more likely to lead to the physiological deterioration of the affected joints
  • The pathophysiology of RA may also go beyond the musculoskeletal system, affecting a wide range of organs including the eyes, heart, lungs, skin and blood vessels

Complications linked to PMR and RA

PMR may be co-occurring with, or may lead to a condition referred to as Giant Cell Arteritis (GCA). GCA, also referred to as Temporal Arteritis (TA), is a disease whereby the blood vessels in the head, neck and arms are inflamed. The resulting symptoms include blurred or double vision, jaw pain and headaches.^10,11 PMR also elevates the risk of developing cardiovascular diseases.

RA on the other hand has a myriad of complications. This is because RA also affects many other parts of the body, including vital organs. Individuals with RA are more likely to develop diabetes and cardiovascular diseases.

RA patients are also likely to be affected by subcutaneous nodules which are lumps of varying sizes, from pea-sized to the size of a lemon.¹² These subcutaneous nodules, also referred to as rheumatoid nodules, are most likely to occur around the joints that are most subject to pressure and trauma. People affected by RA are also likely to be affected by cancer, particularly non-Hodgkin’s lymphoma. The progression of RA may also lead to serious health challenges and disability.

Diagnosis

In diagnosis, the confirmation of PMR and RA requires that multiple factors be considered to ensure accuracy. This is because PMR and RA are quite similar to each other in clinical manifestation. Additionally, they may mimic a variety of other diseases such as osteoarthritis and gout. The medical examinations involved in diagnosis include blood (serological) tests, radiological assessments and identifying the joints involved.

Diagnostic criteria for PMR

The diagnosis of PMR includes a provisional point system to ensure differential diagnosis. This point system was published by the American College of Rheumatology and the European League Against Rheumatism (ACR/EULAR) in 2012.¹³

Basically, this classification system entails a list of PMR symptoms/criteria, with each symptom/criterion being assigned a number of points. So, if a patient aged 50 years or older presents with symmetrical shoulder pain accompanied by a high content of C-reactive protein and an elevated erythrocyte sedimentation rate (ESR), they should be assessed for possible PMR using this system.

An elevated ESR and C-reactive protein reading signal the presence of an inflammatory condition in the body. In this assessment, if the patient also has a variety of other PMR symptoms/criteria adding to 4 points, they should be classified as having PMR. If ultrasonography (ultrasound) is used in diagnosis, the patient should have at least 5 points to be classified as being PMR-positive. Listed here are the symptoms/criteria concerned and the number of points they each carry.¹⁰

• Stiffness in the morning that lasts for more than 45 minutes is equal to 2 points
• A limited range of motion or hip pin equal to a single point
• If the blood is negative for the rheumatoid factor or anti-citrullinated proteins, two points should be added
• If no other joints besides the shoulders are affected, one point should be added
• If ultrasonography detects subdeltoid bursitis in one shoulder, tenosynovitis in the biceps and at least one hip affected by synovitis or trochanteric bursitis, a point should be added
  • Subdeltoid bursitis refers to the inflammation of fluid-filled sacs (bursae) that are found in the shoulder joint, acting as shock absorbers for nearby bones, muscles and tendons
  • Trochanteric bursitis refers to the inflammation of the bursae in the hip joint
• One point should also be added if ultrasonography also detects subdeltoid synovitis in both shoulders, bicep tenosynovitis and glenohumeral synovitis

Diagnostic criteria for rheumatoid arthritis

The diagnosis of RA also entails a point system from the ACR/EULAR.¹⁴ There are four categories of criteria/symptoms used in the diagnosis of RA, with each criterion/symptom being assigned a number of points. Patients having a score of at least 6 points are classified as having RA.

Even though not included in the classification criteria for diagnosing RA, it is worth noting that there are 4 stages of the disease. These stages speak to the level of deterioration in the joints affected, with stage 1 RA being a healthy joint and stage 4 being severe RA with considerable deterioration. X-rays are used in examining the joints.¹

Joint involvement

• If 2 to 10 of the larger joints are involved, a point should be added
  • The larger joints are the shoulders, hips, elbows, knees and ankles
• If between 1 and 3 joints of the fingers and toes are involved, add 2 points
• If between 4 and 10 of the small joints are involved, 2 points should be added
• If more than 10 joints are involved, with at least one 1 small joint being also affected, 5 points should be added

Blood tests specific for the rheumatoid factor or anti-citrullinated protein

The rheumatoid factor and anti-citrullinated protein are antibodies that are present in the blood when there is autoimmunity.^1,15 Autoimmunity refers to when the body attacks its tissues.

• If the levels of rheumatoid factor and anti-citrullinated protein are low, 2 points are added
• If the levels of rheumatoid factor and anti-citrullinated protein are high, 3 points are added

Blood tests specific for the erythrocyte sedimentation rate and C-reactive protein

In the case of RA, a high ESR and C-reactive protein reading equals 1 point

Longevity of symptoms

If symptoms persist for 6 weeks or more, a single point should be added

Treatment and management 

Treatment of PMR

PMR is initially treated with a moderate to high dose of corticosteroids. A prime example of corticosteroids is prednisone. The dosage is gradually decreased over time as symptoms recede, with the treatment being administered for at least a year.⁹ In cases of relapse during treatment, the patient should revert to a high dose of treatment with a gradual reduction in dosage. A disease-modifying antirheumatic drug (DMARD) such as methotrexate may also be used.³

Treatment of RA

RA is treated using DMARDs such as methotrexate. Methotrexate is the initial drug administered following diagnosis and in managing the disease over the long term.^1,9 DMARDs may also be administered with other classes of drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs) to address pain and inflammation. In some patients experiencing flares of RA, corticosteroids such as prednisone may be described. Other types of immunomodulatory drugs in place of or in combination with DMARDs may be administered.¹⁶ 

FAQs

Are there any differences between polymyalgia rheumatica and rheumatoid arthritis?

Both polymyalgia rheumatica and rheumatoid arthritis affect the musculoskeletal system, especially the joints. However, they have different patterns in terms of the joints they affect.

Does polymyalgia rheumatica eventually turn into rheumatoid arthritis?

There are instances whereby patients who are initially diagnosed with polymyalgia rheumatica are later discovered to be having rheumatoid arthritis. This is due to the similarities between the two diseases.

Can polymyalgia rheumatica and rheumatoid arthritis occur simultaneously?

It is highly improbable that a single individual may be affected by both polymyalgia rheumatica and rheumatoid arthritis at the same time.

What are the red flags to look out for in polymyalgia rheumatica?

The red flag symptoms of polymyalgia rheumatica include headaches and jaw pain.

What are the red flags to look out for in rheumatoid arthritis?

Red flag symptoms of rheumatoid arthritis include painful and swollen joints.

Summary

PMR and RA are inflammatory diseases that affect the muscles and joints in the body. Their causes are unknown but there are associated risk factors such as gender, age, ethnicity and genetics. The symptoms of both PMR and RA tend to be nonspecific. As such, these diseases may be mistaken for each other or other joint and muscle-related diseases.

However, some distinguishing factors may be used to differentiate between PMR and RA. There are also diagnosis guidelines that may be used to ensure that PMR and RA are diagnosed correctly. In terms of treatment, PMR symptoms are addressed using corticosteroids which are administered for at least 12 months. DMARDs may also be used to treat PMR.

On the other hand, RA is treated with DMARDs as a first line of treatment. A good example of a DMARD is methotrexate. If treated accordingly, PMR is not a life-threatening disease. With RA, the disease is progressive and may significantly worsen the quality of life as time progresses.