Introduction

Polymyalgia Rheumatica (PMR) and Giant Cell Arteritis (GCA) are two conditions that seem to be closely related but vary in their pathophysiology. They affect millions of people worldwide and can have overlapping symptoms, although the hallmark presentations of each of these conditions are distinct. In this article, we will explore what the two conditions are and provide an insight into their causes, symptoms, diagnosis and management. 

Understanding Polymyalgia Rheumatica

According to the British Society of Rheumatology, PMR is the most common inflammatory rheumatic disease in the elderly population.¹ As such, it presents exclusively in people aged 50 or over, and its incidence increases with age. The lifetime risk of PMR in people assigned female at birth (AFAB) is 2.5%, compared to a 1.7% risk in people assigned male at birth (AMAB), so it’s more likely to present in people AFAB.²

Pathophysiology and causes of PMR

The pathophysiology of this condition revolves around inflammation of the joints; particularly extracapsular structures (structures that join two ligaments) and the synovium.³ Synovium refers to the soft tissue that lines the inner surface of joints. When inflammation is contained within that area, it is known as synovitis. This is not the same as arthritis, which is a broader term and involves inflammation or pain in the joint, with or without synovial inflammation.

The cause of PMR is essentially unknown. As with the many conditions that we lack sufficient understanding of, PMR is thought to involve a combination of environmental and genetic risk factors. Interestingly, it commonly presents in summer, so potential seasonal variation may be at play. It has also been observed more often in populations living at northern latitudes, such as Scandinavia.

Presentation

The typical presentation is bilateral morning stiffness and ache, in several major joints, such as the shoulder, neck and pelvic girdle. It is important to note that stiffness is a hallmark for this condition, but not weakness, as it’s not considered to be indicative of PMR and usually implies a different diagnosis. Stiffness may last more than 30 minutes and can make several activities and movements particularly difficult. These include:

• Getting out of bed (or rolling over if symptoms are persistent)
• Standing up from a seated position 
• Shoulder movements - brushing or washing hair

PMR tends to have a fast onset.⁴ It’s not something that builds gradually over years (like osteoarthritis) and patients often recognise that there was no particular cause for their presentation. There may be some accompanying systemic signs, which occur in about 40% of patients. Affected individuals may report a “flu-like illness” during the first 2 weeks of the condition. Other signs may include fatigue, weight loss and depression.

Diagnosis

A physical examination may not reveal much, as the joints are not usually swollen. If there are some findings, they may be discomfort, stiffness or restricted range of movement (although this is more likely in severe cases).

The key investigation for PMR, however, is performing a blood test.⁵ Clinicians would request some blood tests, such as complete blood counts (CBC), thyroid function tests (TFTs) and rheumatological screens, to rule out other causes. But, it is precisely the inflammatory markers and creatine kinase (CK) that are essential for the diagnosis. Inflammatory markers include, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR). Raised inflammatory markers, particularly ESR, are in support of a PMR diagnosis. However, CK should be normal.

Other investigations may include x-rays, ultrasound and magnetic resonance imaging (MRI), but a diagnosis of PMR can be made without the need for imaging. 

Understanding giant cell arteritis

GCA is also known as temporal arteritis. Much like PMR, it affects patients over the age of 50 and has a higher AFAB to AMAB incidence ratio. Many patients with GCA will also have some polymyalgic symptoms, and may have already had a diagnosis of PMR. 

Pathophysiology and causes of GCA

This condition is a form of vasculitis, i.e., immune-mediated inflammation that affects the arterial wall.⁶ It specifically affects medium and large-sized arteries, such as branches of the carotid artery, which supply areas of the head and face. The superficial temporal, occipital and ophthalmic arteries are amongst the vessels that may be affected. Where inflammation occurs, there will be pain and tenderness in the associated areas. In later stages, pulses may be weak/lost and the scalp may look red. 

Similar to PMR, the cause is unknown, but it also has a higher incidence in Northern European countries.

Presentation

A typical presentation of GCA is an elderly patient with a new onset headache and scalp tenderness. The onset of the condition is usually sudden, so patients will have a short history of these symptoms. Although scalp tenderness is often mentioned in association with GCA, it’s only documented in around 25% of cases.⁶ Affected individuals may also report some neck discomfort, jaw claudication/pain and fatigue. 

A potential complication of GCA which prompts clinicians to treat the condition as soon as it’s suspected is visual loss. Patients may experience painless loss of vision or double vision. Any visual changes will be regarded as critical, as sudden permanent blindness can occur, if medical attention is not sought.

Diagnosis

GCA can be treated promptly, if it’s the suspected diagnosis. However some examinations include performing an eye exam to assess visual acuity and examining the temporal arteries. Normal arterial and visual examinations do not exclude a diagnosis of GCA.

Like PMR, blood tests for inflammatory markers are useful for the diagnosis. A normal ESR and CRP will therefore make a diagnosis of GCA unlikely. But a temporal artery biopsy is the definitive diagnostic test. The histological features of the sample/biopsy will reveal if an inflammatory process is occurring.

Management of PMR and GCA

Steroids are the mainstay of treatment for both PMR and GCA. If GCA is suspected, corticosteroids should be started immediately. Depending on whether the patient has visual loss/disturbance or not, high-dose prednisolone or methylprednisolone may be given.⁷ Symptoms should reduce significantly within the first few days, but medications may be continued for much longer, until the disease is settled and inflammatory markers have resolved.

Unlike GCA, if PMR is suspected, it does not require immediate treatment with steroids. Usually, low-dose steroids are prescribed and this could be tapered over the treatment course. Again, as with GCA, if symptoms do not improve within one week of steroid use, then an alternative diagnosis would be considered. Relapse is common in PMR but patients respond well to a restart of steroid medications.⁸ However about 15% of patients with PMR may develop GCA. 

Other aspects to the management of PMR and GCA, include calcium and vitamin D supplements and potentially bisphosphonates, to reduce the risk of steroid-induced osteoporosis. Physiotherapy may be helpful in some patients whose function and mobility are affected. 

Summary

There is an evident association between PMR and GCA. The increasingly-common perception in recent literature is that the two conditions are different manifestations of the same disorder. This explains the considerable overlap in symptoms, progression and management. However, there still remains much uncertainty in this statement as the underlying pathology for the two conditions are different.