What is Polymyalgia Rheumatica (PMR) and what are the diagnostic tests for it?

Polymyalgia Rheumatica: Diagnosis and Diagnostic Tests

Polymyalgia rheumatica (PMR) is an inflammatory rheumatic disease affecting adults over 50 years of age, characterized by bilateral pain and stiffness in the shoulder girdle, neck, and pelvic girdle with elevated inflammatory markers and rapid response to glucocorticoid therapy. 1, 2

Clinical Characteristics

• PMR is the second most common inflammatory rheumatic condition in older adults after rheumatoid arthritis 1
• Typical presentation includes:
  • Bilateral aching pain in the shoulder girdle 2, 3
  • Morning stiffness lasting more than 30 minutes 2
  • Neck and hip girdle involvement 3
  • Symptoms typically develop in individuals over 50 years of age 1, 4
• Systemic inflammatory response is present in most cases 1

Diagnostic Approach

• There is no single pathognomonic test for PMR diagnosis 2, 3
• Diagnosis is primarily based on:
  • Characteristic clinical presentation 3
  • Laboratory evidence of systemic inflammation 4
  • Rapid response to low-dose glucocorticoids 4
  • Exclusion of other conditions that can mimic PMR 2, 3

Laboratory Tests

• Elevated inflammatory markers:
  • Erythrocyte sedimentation rate (ESR) 1, 4
  • C-reactive protein (CRP) 1, 4
• Note: High levels of inflammatory markers at diagnosis may influence disease outcomes 5

Imaging Studies

• Musculoskeletal ultrasound is increasingly used in PMR evaluation 6
  • Can help identify characteristic inflammatory changes in shoulder and hip girdles 6
  • Assists in distinguishing PMR from other conditions with similar presentations 2
• Other imaging modalities may be used to exclude alternative diagnoses 2

Classification Criteria

• In 2012, the European League Against Rheumatism (EULAR) and American College of Rheumatology (ACR) developed provisional classification criteria for PMR 4
• These criteria include:
  • Age ≥50 years 4
  • Bilateral shoulder pain 4
  • Abnormal inflammatory markers (ESR and/or CRP) 4
  • Morning stiffness >45 minutes 4
  • Hip pain or limited range of motion 4
  • Absence of rheumatoid factor or anti-citrullinated protein antibodies 4
  • Absence of other joint involvement 4

Differential Diagnosis

• Several conditions can mimic PMR and must be excluded:
  • Giant cell arteritis (GCA) - commonly associated with PMR 1
  • Elderly-onset rheumatoid arthritis (EORA) 1, 3
  • Other autoimmune, infectious, malignant, and endocrine disorders 1
  • Recently reported cases associated with immune checkpoint inhibitor therapy 1

Therapeutic Response as Diagnostic Test

• A rapid response to low-dose glucocorticoids (15-20 mg prednisone equivalent daily) is considered a diagnostic feature 3
• Lack of response should prompt reconsideration of the diagnosis 2, 3

Common Pitfalls in Diagnosis

• Failure to exclude other conditions that can mimic PMR 2
• Over-reliance on inflammatory markers alone (they may be normal in some cases) 4
• Not considering associated conditions like giant cell arteritis 1
• Inadequate follow-up to confirm diagnosis through treatment response 3

Monitoring

• Regular assessment of disease activity and treatment response is essential 5
• Monitoring for glucocorticoid-related adverse effects is crucial, especially in elderly patients 1, 2