Polymyalgia Rheumatica vs Polymyositis

Polymyalgia Rheumatica vs Polymyositis - Key Differences

Understanding Polymyalgia Rheumatica and Polymyositis

Polymyalgia rheumatica (PMR) and polymyositis are two rheumatic conditions that cause muscle pain and stiffness. Though they share some similarities, there are important differences between these disorders in terms of symptoms, disease progression, and treatment.

What is Polymyalgia Rheumatica?

Polymyalgia rheumatica (PMR) is an inflammatory disorder that leads to muscle pain and stiffness, especially in the shoulders, neck and hips. Some of the key features of PMR include:

Onset typically after age 50
Aching, throbbing pain in shoulders, neck and hips
Stiffness and difficulty moving affected areas
Symptoms usually worst in mornings
Fatigue and possible fever
No skin rashes

PMR is considered a type of vasculitis - inflammation of blood vessels - that affects small and medium blood vessels supplying muscles. This impacts muscle tissue, leading to the characteristic pain and stiffness. Though the exact cause is unknown, genetics and immune system dysfunction may play a role.

Diagnosing Polymyalgia Rheumatica

There are no definitive laboratory tests that can conclusively diagnose polymyalgia rheumatica. Doctors primarily rely on a patient's clinical presentation and response to treatment to make the diagnosis. Some findings that may support a PMR diagnosis include:

Elevated inflammatory markers like ESR and CRP
Imaging showing inflammation around shoulders/hips
Rapid improvement with corticosteroid treatment

It's important to rule out other potential causes, so doctors may run tests to exclude conditions like rheumatoid arthritis, fibromyalgia or thyroid disorders. A prompt PMR diagnosis is essential since untreated disease can lead to disability.

Treatment for Polymyalgia Rheumatica

Polymyalgia rheumatica generally responds very well to corticosteroid treatment, with most patients experiencing significant relief within days to weeks. Typical PMR treatment involves:

Low-dose corticosteroids (prednisone) to reduce inflammation
Eventually tapering corticosteroids over 1-2 years
Second-line agents if needed, like methotrexate
Activity modification when symptoms are worse
Physical therapy once acute inflammation improves

With appropriate treatment, most people achieve full remission within 1-2 years and are able to stop therapy. Relapses occur in up to half of patients but often respond to increasing steroids temporarily.

What is Polymyositis?

Polymyositis is an inflammatory myopathy, a disorder causing muscle inflammation and weakness. Some key features include:

Onset possible at any age, but more common in adults
Progressive weakness more pronounced in shoulders/hips
Muscle pain and tenderness common
Fatigue and difficulty swallowing possible
May have skin rashes

In polymyositis, the body's immune system attacks muscle fibers for unknown reasons, leading to damage and weakness. It may affect multiple muscles groups, particularly those closest to the trunk like shoulders and hips.

Getting Diagnosed with Polymyositis

Obtaining a polymyositis diagnosis can involve multiple steps, including:

Physical exam assessing muscle strength
Blood tests checking muscle enzymes (CK, aldolase)
Electromyography showing impaired electrical activity in muscles
MRI scans revealing muscle inflammation
Muscle biopsy confirming inflammatory cell invasion

These tests help characterize the pattern of muscle involvement and cell changes consistent with polymyositis to distinguish it from other neuromuscular disorders.

Treating Polymyositis

Corticosteroids like prednisone are first-line treatments for polymyositis as well. But compared to PMR, higher doses are often needed for longer periods, sometimes years. Other polymyositis treatments include:

Immunosuppressant medications (azathioprine, methotrexate)
Intravenous immunoglobulin (IVIg)
Plasma exchange in severe cases
Physical and/or speech therapy

These more intensive treatments aim to control disease activity that can persist and lead to permanent muscle damage without adequate immune suppression. Supportive therapy also plays an important role.

Key Differences Between Polymyalgia Rheumatica and Polymyositis

Despite some overlapping features like shoulder and hip involvement, there are critical distinctions between polymyalgia rheumatica and polymyositis:

Age of Onset

PMR very rarely occurs before age 50, while polymyositis can develop at any age. PMR peaks in incidence between ages 70-80.

Speed of Progression

Polymyalgia symptoms generally come on quickly over days to weeks and improve rapidly with treatment. In contrast, polymyositis may evolve over longer periods and is more resistant to treatment.

Strength/Function

Pain and stiffness limit range of motion with PMR but strength remains intact. Polymyositis directly causes muscle weakness leading to functional disability like trouble climbing stairs or combing hair.

Skin Findings

PMR does not cause rashes. A quarter of people with polymyositis have typical skin manifestations like Gottron’s papules over the knuckles.

Laboratory Findings

Inflammatory markers like ESR and CRP are elevated in most PMR patients but can be normal in polymyositis. Muscle enzyme levels are almost always abnormally high with polymyositis.

Treatment Response

PMR treatment relies on low-moderate dose steroids tapered over 1-2 years, resulting in disease control in most patients. Polymyositis often requires other intensive immunosuppressive drugs added to higher dose steroids.

Outlook

With treatment, 70-90% of PMR patients achieve sustained remission off medications. Polymyositis follows a relapsing-remitting course in most individuals despite therapy.

Takeaways

Polymyalgia rheumatica causes severe inflammatory muscle pain while polymyositis leads to muscle weakness.
PMR onset after age 50 while polymyositis can develop at any age.
PMR generally improves rapidly with low-dose steroids but polymyositis treatment is more complex.
Distinguishing between these two rheumatic syndromes is vital for appropriate treatment.

In summary, quickly differentiating between polymyalgia rheumatica and polymyositis based on clinical presentation can facilitate tailored management of these two challenging inflammatory muscle conditions that share some overlapping features but differ in critical aspects of disease course and treatment response.

FAQs

What is the main symptom of polymyalgia rheumatica?

The most common symptom of polymyalgia rheumatica (PMR) is muscle pain and stiffness, particularly in the shoulders, neck and hips. Patients typically experience severe aching and throbbing pain, worse in the mornings and improving with activity.

What causes muscle weakness in polymyositis?

In polymyositis, the body’s immune system mistakenly attacks healthy muscle tissue. This causes inflammation and damage to muscle fibers, leading to progressive weakness that is usually most pronounced in the shoulders and hips.

How are polymyalgia and polymyositis treated?

Both conditions are treated with corticosteroids like prednisone to suppress inflammation. But polymyositis often requires long-term high dose steroids in combination with other immunosuppressant medications due to its relapsing nature.

What is the long-term outlook for these conditions?

With treatment, most patients with polymyalgia rheumatica achieve sustained remission within 1-2 years. In contrast, polymyositis follows a chronic relapsing course in many patients despite therapy.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.