Stiffness in Polymyalgia Rheumatica vs Polymyositis
Yes, significant stiffness is a hallmark feature of polymyalgia rheumatica (PMR), particularly morning stiffness, whereas polymyositis typically presents with muscle weakness without prominent stiffness.
Polymyalgia Rheumatica: Stiffness as a Core Feature
Morning stiffness is one of the defining characteristics of PMR and serves as a key diagnostic criterion. 1, 2, 3
Clinical Presentation of Stiffness in PMR
- PMR presents with acute, predominantly bilateral shoulder and/or hip pain with morning stiffness that is severe and functionally limiting 1
- The stiffness typically affects the shoulder girdle, neck, and pelvic girdle muscles, with onset that may be acute or develop over a few days to weeks 3, 4
- Longer duration of morning stiffness at baseline is linked with worse function and quality of life at 12 months, indicating its prognostic significance 1
- The stiffness is characteristically worse with movement and improves throughout the day, though this accentuation pattern may be absent in atypical presentations 5
Diagnostic Significance
- Morning stiffness lasting more than 1 month in at least 2 of 3 areas (neck, shoulder, pelvic girdle) is part of the diagnostic criteria for PMR 5
- The presence of bilateral shoulder pain with morning stiffness, along with age >50 years and elevated inflammatory markers, forms the initial diagnostic triad 6
- Possible swelling of the hands and knees may accompany the stiffness in some PMR presentations 1, 7
Polymyositis: Weakness Without Prominent Stiffness
Polymyositis is characterized by proximal muscle weakness rather than stiffness, and this distinction is critical for differential diagnosis.
Key Differentiating Features
- Myalgia secondary to myositis should be ruled out when evaluating stiffness, as the clinical presentations differ fundamentally 1
- Creatine kinase (CK) should be normal in PMR, which differentiates it from inflammatory myositis where CK is typically elevated 6
- Polymyositis presents with progressive proximal muscle weakness affecting activities like climbing stairs or lifting objects, rather than the pain and stiffness pattern seen in PMR 4
Clinical Algorithm for Distinguishing the Two Conditions
Initial Assessment
- Evaluate whether the primary complaint is stiffness with pain (suggests PMR) versus weakness without prominent stiffness (suggests polymyositis) 1, 6
- Check CK levels: normal in PMR, elevated in polymyositis 6
- Assess inflammatory markers (ESR/CRP): typically markedly elevated in PMR (ESR >40 mm/h), variable in polymyositis 6, 5
Response to Treatment
- PMR responds promptly to low-dose glucocorticoids (12.5-25 mg prednisone daily), often within days 3, 8
- Polymyositis requires higher doses of immunosuppression and responds more slowly 4
- Lack of rapid response to low-dose prednisone should prompt reconsideration of the PMR diagnosis 1
Common Pitfalls to Avoid
- Do not attribute muscle symptoms to PMR if CK is elevated—this suggests myositis and requires different management 6
- Atypical presentations lacking prominent morning stiffness or showing continuous diffuse aching rather than movement-related pain should raise suspicion for alternative diagnoses, including malignancy or other rheumatic conditions 5
- In patients presenting with polymyalgia symptoms, consider that up to 11% may have conditions mimicking PMR, with rheumatic diseases and malignancies being most common 5
- Peripheral inflammatory arthritis in PMR may be associated with higher relapse rates and may warrant specialist referral 7