Non Articular Musculoskeletal Pain

Introduction

Non-articular musculoskeletal pain refers to pain arising from structures other than the joint capsule and synovium. This includes soft tissues such as muscles, fascia, tendons, ligaments, and bursae. For the MCCQE1, differentiating these conditions from articular pathology (like Rheumatoid Arthritis or Osteoarthritis) is a critical Medical Expert skill.

This guide focuses on high-yield conditions including Fibromyalgia, Polymyalgia Rheumatica (PMR), Complex Regional Pain Syndrome (CRPS), and Myofascial Pain Syndrome. Understanding the Canadian approach to management—emphasizing non-pharmacological interventions and Choosing Wisely recommendations—is essential for exam success.

Articular vs. Non-Articular Pain

Before diagnosing specific conditions, a candidate must distinguish the origin of the pain.

Comparison Table

Fibromyalgia

Fibromyalgia is a chronic pain syndrome characterized by widespread musculoskeletal pain, fatigue, sleep disturbances, and cognitive dysfunction (“fibro fog”). It affects approximately 2-3% of the Canadian population, predominantly females.

Diagnosis (ACR 2016 Criteria)

The diagnosis is clinical. The historical “tender point exam” (11/18 points) is no longer required for diagnosis but may still be tested in historical contexts or physical exam checklists.

Current Criteria require:

1. Generalized pain (in at least 4 of 5 regions).
2. Symptoms present for at least 3 months.
3. Widespread Pain Index (WPI) and Symptom Severity (SS) scale scores meeting specific thresholds.
4. Exclusion of other disorders that could explain the pain (though it can coexist with RA or SLE).

Management Approach

Management in the Canadian context is multidisciplinary.

Polymyalgia Rheumatica (PMR)

PMR is an inflammatory condition affecting the shoulder and hip girdles, almost exclusively seen in patients >50 years old (average age 70).

Clinical Presentation

• Bilateral pain and stiffness in shoulder and pelvic girdles.
• Morning stiffness lasting >45 minutes (often hours).
• Systemic symptoms: Low-grade fever, fatigue, weight loss.
• No significant muscle weakness (pain may limit effort, but true strength is preserved).

Investigation Findings

• ESR: Markedly elevated (>40 mm/hr, often >80).
• CRP: Elevated.
• CK: Normal (differentiates from polymyositis/statin-induced myopathy).
• RF/CCP: Negative.

Association with Giant Cell Arteritis (GCA)

Treatment Strategy

Complex Regional Pain Syndrome (CRPS)

Formerly known as Reflex Sympathetic Dystrophy (RSD). A chronic pain condition often following trauma (fracture, surgery) that is disproportionate to the inciting event.

• Type I: No nerve lesion.
• Type II: Defined nerve lesion present.

The “STAMP” Mnemonic for Clinical Features

• Sensory: Allodynia (pain from non-painful stimuli), hyperalgesia.
• Trophic changes: Skin, hair, nail changes.
• Autonomic: Swelling, edema, sweating anomalies.
• Motor: Weakness, contractures, atrophy.
• Pain: Burning, disproportionate to injury.

Management

• Early mobilization and Physical Therapy (desensitization) are crucial.
• Pharmacotherapy: Gabapentinoids, TCAs, Bisphosphonates (for bone loss), topical lidocaine.
• Referral to chronic pain clinic.

Canadian Guidelines & Choosing Wisely

Adherence to Choosing Wisely Canada recommendations is highly tested.

1. Don’t prescribe opioids for Fibromyalgia.
   • Reasoning: Evidence shows lack of efficacy and high risk of harm.
2. Don’t order ANA or specialized autoantibodies (ENA) as a screening test for non-specific musculoskeletal pain.
   • Reasoning: High false-positive rate leads to unnecessary anxiety and referrals. Only order if there is clinical suspicion of connective tissue disease (e.g., photosensitivity, Raynaud’s, inflammatory arthritis).
3. Don’t order imaging for non-specific low back pain (part of myofascial pain) unless red flags are present.
   • Red Flags: Age >50 or <20, history of cancer, constitutional symptoms, recent bacterial infection, IV drug use, immunosuppression, significant trauma, or progressive neurologic deficit.

Key Points to Remember for MCCQE1

• Fibromyalgia: Normal labs, central sensitization, treat with exercise/CBT/TCAs. Avoid opioids.
• PMR: Age >50, high ESR, shoulder/hip stiffness, rapid response to low-dose prednisone. Always rule out GCA.
• Polymyositis vs. PMR: Polymyositis has painless weakness and elevated CK. PMR has pain/stiffness without true weakness and normal CK.
• Investigation: In a patient with diffuse pain and “tender points,” a positive ANA is likely a false positive if no other specific symptoms exist.
• Management: The Canadian healthcare system emphasizes primary care management for these conditions, reserving Rheumatology consults for diagnostic uncertainty or inflammatory arthritis.

Sample Question

Case Presentation

A 73-year-old female presents to your family medicine clinic complaining of a 3-week history of severe aching and stiffness in her neck, shoulders, and hips. She reports that the stiffness is worse in the morning and lasts for about 2 hours. She has difficulty brushing her hair and rising from a chair due to pain, but denies specific muscle weakness. She reports a low-grade fever and a 2 kg weight loss over the last month. She denies headache, visual changes, or jaw pain. Physical examination reveals limited active range of motion in the shoulders and hips due to pain, but passive range of motion is preserved. There is no synovitis or joint swelling detected in the peripheral joints.

Laboratory results:

• Hemoglobin: 110 g/L (Normal: 120-160)
• Leukocytes: 8.5 x 10^9/L (Normal: 4.0-11.0)
• Creatine Kinase (CK): 95 U/L (Normal: 30-170)
• ESR: 88 mm/hr (Normal: <30)
• Rheumatoid Factor: Negative

Which of the following is the most appropriate initial management step?

Options

• A. Initiate high-dose prednisone (60 mg daily)
• B. Initiate low-dose prednisone (15 mg daily)
• C. Prescribe naproxen 500 mg BID and physiotherapy
• D. Order an MRI of the cervical spine and shoulders
• E. Start methotrexate 15 mg weekly

Explanation

The correct answer is:

• B. Initiate low-dose prednisone (15 mg daily)

Detailed Analysis

Diagnosis: The clinical presentation is classic for Polymyalgia Rheumatica (PMR).

• Demographics: Patient is >50 years old.
• Symptoms: Bilateral shoulder and hip girdle pain/stiffness, significant morning stiffness (>45 mins).
• Systemic signs: Weight loss, anemia of chronic disease (mild Hb drop), high ESR.
• Negative findings: Normal CK rules out myositis; lack of peripheral synovitis and negative RF makes RA less likely; lack of headache/visual symptoms makes GCA less likely.

Reasoning for Options:

• A. Initiate high-dose prednisone (60 mg daily): This is the treatment for Giant Cell Arteritis (GCA). Since the patient denies headache, jaw claudication, and visual changes, high-dose steroids are unnecessary and carry higher risks.
• B. Initiate low-dose prednisone (15 mg daily): This is the standard of care for PMR. A rapid and dramatic improvement (usually within days) confirms the diagnosis.
• C. Prescribe naproxen: NSAIDs may provide mild relief but are generally ineffective for the significant inflammation associated with PMR and are not first-line therapy.
• D. MRI: Not indicated. The diagnosis is clinical supported by elevated inflammatory markers.
• E. Methotrexate: This is a steroid-sparing agent used in resistant cases or during tapering difficulties, but it is not the initial induction therapy.

References

1. RheumInfo. (2023). Polymyalgia Rheumatica (PMR) & Fibromyalgia. Available at RheumInfo.com .
2. Choosing Wisely Canada. (2023). Rheumatology: Five Things Physicians and Patients Should Question.
3. Medical Council of Canada. (2023). MCCQE Part I Objectives: Musculoskeletal System.
4. Fitzcharles, M.A., et al. (2013). 2012 Canadian Guidelines for the diagnosis and management of fibromyalgia syndrome. CMAJ.
5. Dejaco, C., et al. (2015). 2015 EULAR/ACR recommendations for the management of polymyalgia rheumatica. Annals of the Rheumatic Diseases.