Polymyalgia Rheumatica

Detailed Overview

PMR is one of the most common inflammatory rheumatic diseases in the elderly. It is closely associated with Giant Cell Arteritis (GCA); roughly 15-20% of patients with PMR develop GCA, and 40-50% of GCA patients have PMR symptoms. The disease does not cause true muscle weakness, but rather pain so severe that it limits movement. PMR responds dramatically and rapidly to low-dose systemic corticosteroids, which is considered both therapeutic and diagnostically supportive. Without treatment, it significantly impairs quality of life.

Epidemiology & Demographics

Incidence is 50 per 100,000 individuals over age 50. Almost never occurs before age 50. Incidence peaks in the 70s. Females are affected 2-3 times more often than males. More common in populations of Northern European descent.

Etiological Mechanism

Unknown, but suspected to be an interplay of genetic predisposition (HLA-DRB1 alleles) and environmental triggers (possibly viral infections like adenovirus or parvovirus B19) leading to immune system dysregulation.

Primary Causes

An autoimmune inflammatory response targeting the synovium and bursae of large proximal joints.

• Age over 50: The most significant risk factor; peak onset is between 70 and 80 years.
• Female Sex: Women are two to three times more likely to develop PMR than men.
• Northern European Ancestry: Highest rates are seen in Scandinavian countries and populations of matching descent.

PMR is characterized by synovitis, bursitis, and tenosynovitis of the proximal joints (especially subacromial/subdeltoid bursitis and trochanteric bursitis). It is a systemic macrophage and T-cell mediated immune response. An increase in pro-inflammatory cytokines, particularly Interleukin-6 (IL-6), drives the systemic acute-phase response, causing elevated ESR and CRP. Unlike rheumatoid arthritis, PMR does not result in erosive joint destruction or autoantibody production (RF/anti-CCP are negative). The pain is due to inflammation of the periarticular structures rather than the muscle fibers themselves, explaining the lack of elevated muscle enzymes (normal CK).

Characteristic Clinical Presentation

• Proximal Muscle Aching: Bilateral, symmetric pain in the shoulders, neck, and pelvic girdle (hips/thighs).
• Morning Stiffness: Profound stiffness lasting >45 minutes after waking up, making it difficult to get out of bed or dress.
• Systemic Symptoms: Low-grade fever, fatigue, malaise, anorexia, and unintended weight loss.
• Distal Manifestations: Mild non-erosive arthritis of wrists or knees, and occasionally carpal tunnel syndrome.

Physical Examination Signs

• Decreased active range of motion in shoulders and hips due to pain.
• Tenderness to palpation over the subacromial or trochanteric bursae.
• Normal muscle strength testing (differentiates from polymyositis), though pain may cause 'give-way' weakness.
• Absence of true joint swelling or effusions typical of RA.

• Giant Cell Arteritis (GCA): Development of cranial arteritis which can lead to permanent irreversible blindness or stroke.
• Glucocorticoid Toxicity: Osteoporosis, weight gain, diabetes, hypertension, and cataracts from prolonged steroid use.
• Functional Decline: Severe physical deconditioning and depression if left untreated.

Diagnostic Criteria & Guidelines

Clinical diagnosis based on age >50, bilateral shoulder/pelvic aching, morning stiffness >45 mins, elevated ESR/CRP, and a rapid, dramatic response to low-dose glucocorticoids within 48-72 hours.

Differential Diagnosis

• Rheumatoid Arthritis (late-onset)
• Polymyositis / Dermatomyositis
• Fibromyalgia
• Multiple Myeloma or occult malignancy
• Hypothyroidism

Laboratory Tests & Biomarkers

• Erythrocyte Sedimentation Rate (ESR): Markedly elevated, typically >40 mm/hr, often >80 mm/hr.
• C-Reactive Protein (CRP): Elevated (e.g., >10 mg/L), often a more sensitive marker than ESR for PMR.
• Creatine Kinase (CK): Strictly NORMAL; rules out primary muscle destruction like polymyositis.
• Rheumatoid Factor (RF) and Anti-CCP: Negative; helps distinguish from elderly-onset Rheumatoid Arthritis.

Imaging Modalities & Findings

• Musculoskeletal Ultrasound: Bilateral subacromial/subdeltoid bursitis, biceps tenosynovitis, and trochanteric bursitis. Strongly supports the diagnosis.
• MRI Shoulders/Hips: Shows periarticular inflammation and bursitis, but usually unnecessary for routine diagnosis.

• Active/Untreated
  Severe stiffness and pain with highly elevated inflammatory markers.
• Remission on Therapy
  Symptoms resolved completely on maintenance low-dose corticosteroids.
• Relapse
  Return of symptoms and rising CRP, typically occurring during steroid tapering.

Second-Line & Adjunctive Therapy

Methotrexate 10-15 mg PO weekly with Folic acid 1 mg daily. Used as a steroid-sparing agent in patients who experience relapses during tapering or have high risk for glucocorticoid toxicity (e.g., severe diabetes, severe osteoporosis).

Surgical & Procedural Management

None indicated for PMR.

Recommended Lifestyle Changes

• Engage in weight-bearing exercise (walking) and resistance training to preserve bone density and muscle mass.
• Dietary modifications to prevent steroid-induced weight gain and hyperglycemia.

Patient Counseling & Advice

Warn the patient NEVER to stop Prednisone abruptly due to the risk of adrenal crisis. Educate them on the symptoms of Giant Cell Arteritis (new severe headaches, jaw pain when chewing, vision changes) and to seek emergency care immediately if they occur.

Follow-Up & Monitoring Schedule

Clinical review and ESR/CRP testing every 4-8 weeks during the tapering phase. Dual-energy X-ray absorptiometry (DEXA) scan at baseline to assess fracture risk, and consider starting a bisphosphonate (e.g., Alendronate) prophylactically.

Preventive Strategies

No known prevention for the disease itself. Prevention focuses on avoiding steroid-induced osteoporosis via calcium, vitamin D, and bisphosphonates.

Excellent prognosis for symptom resolution. The course of the disease typically lasts 1 to 2 years, after which steroids can be successfully stopped in most patients. Relapses occur in about 50% of patients during the taper.