2.3 Chronic Musculoskeletal & Rheumatological Conditions

Section 2.3: Chronic Musculoskeletal & Rheumatological Conditions

1. Osteoarthritis (OA)

Osteoarthritis is a chronic, degenerative joint disorder characterized by progressive loss of articular cartilage, subchondral bone remodeling, osteophyte formation, and mild secondary synovial inflammation.

Clinical Presentation and Differentiation

OA primarily affects weight-bearing joints (knees, hips) and the hands.

• Symptoms: Pain that is characteristically worse with joint use and improved with rest. Morning joint stiffness is brief, typically lasting less than 30 minutes.
• Physical Exam: Joint crepitus, bony enlargement, and limited range of motion. Pathognomonic hand findings include Heberden's nodes at the distal interphalangeal (DIP) joints and Bouchard's nodes at the proximal interphalangeal (PIP) joints, along with squaring of the first carpometacarpal (CMC) joint.
• Radiography: Classic features include asymmetrical joint space narrowing, osteophytes (bony spurs), subchondral sclerosis (increased bone density under the cartilage), and subchondral cysts.

Clinical Management

1. Non-pharmacological: Weight loss (reduces load on weight-bearing joints), low-impact physical therapy (e.g., swimming, cycling to strengthen quadriceps), and assistive devices.
2. Pharmacological:
   • Topical NSAIDs: Topical diclofenac gel is the preferred first-line therapy for knee and hand OA due to its excellent local efficacy and minimal systemic absorption, reducing gastrointestinal and cardiovascular risk.
   • Oral NSAIDs: Reserved for patients who do not respond to topical therapy. Must be co-prescribed with a Proton Pump Inhibitor (PPI) in patients at high risk of gastrointestinal bleeding.
   • Intra-articular Corticosteroids: Indicated for acute, severe pain flares, providing temporary relief (typically 1-3 months).
   • Arthroplasty: Total joint replacement is indicated for patients with end-stage OA who have refractory pain and severe functional impairment.

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2. Gout: Pathophysiology and Therapeutics

Gout is an inflammatory arthritis caused by the deposition of monosodium urate (MSU) crystals in joints and soft tissues, occurring in the setting of chronic hyperuricemia (serum urate > 6.8 mg/dL).

Pathophysiology

Hyperuricemia results from either uric acid overproduction (e.g., myeloproliferative disorders) or, more commonly (90% of cases), renal underexcretion of uric acid. MSU crystals are needle-shaped and exhibit strong negative birefringence under polarized light microscopy.

Acute Gout Flare Management

Flares present as rapid-onset, excruciatingly painful, erythematous, warm, and swollen joints. The first metatarsophalangeal (MTP) joint is affected in over 50% of initial attacks (podagra).

• First-line Agents: Oral NSAIDs (e.g., indomethacin), colchicine, or systemic/intra-articular corticosteroids. Therapy must be initiated within 24 hours of flare onset.
• Colchicine Dosing: Low-dose regimen is preferred: 1.2 mg orally at onset, followed by 0.6 mg one hour later. Dose adjustment is required in renal impairment.
• Clinical Trap: Do not stop or start urate-lowering therapy (ULT) during an acute flare. If the patient is already on ULT, continue it at the same dose. If the patient is not on ULT, wait 2-4 weeks after the flare has completely resolved before initiating it, as rapid fluctuations in serum urate levels can prolong or worsen the acute attack.

Chronic Gout and Urate-Lowering Therapy (ULT)

• Indications: Recommended for patients with ≥ 2 flares per year, tophi, radiographic joint damage, or CKD stage 3 or worse.
• First-line ULT: Allopurinol (a xanthine oxidase inhibitor). The starting dose is low (100 mg/day, lower in CKD) and titrated to reach a target serum urate level of < 6.0 mg/dL (or < 5.0 mg/dL in patients with tophaceous gout).
• HLA-B*5801 Allele Screening: Strongly recommended before initiating allopurinol in patients of Han Chinese, Thai, or Korean descent, and Gulf Arab populations. The presence of this allele is strongly associated with Allopurinol Hypersensitivity Syndrome (a life-threatening reaction featuring Stevens-Johnson Syndrome/toxic epidermal necrolysis, fever, and acute kidney injury).
• Flare Prophylaxis: When starting or titrating ULT, a low-dose prophylactic agent (e.g., low-dose colchicine 0.6 mg daily) must be co-prescribed for 3 to 6 months to prevent mobilizing flares as crystals dissolve.
• Alternative ULT: Febuxostat (carries a FDA boxed warning for cardiovascular mortality risk in patients with established cardiovascular disease).

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3. Osteoporosis: Screening and Bisphosphonates

Osteoporosis is a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to increased bone fragility and susceptibility to fractures.

Screening and Diagnosis

Screening is performed via Dual-Energy X-ray Absorptiometry (DXA) scanning.

• Indications: All women ≥ 65 years and men ≥ 70 years. Younger postmenopausal women and men aged 50-69 with clinical risk factors (e.g., chronic glucocorticoid use, rheumatoid arthritis, history of smoking or high alcohol intake) should be screened. The FRAX tool is used to calculate 10-year fracture probability to guide treatment.
• T-score Interpretation:
  • T-score ≥ -1.0: Normal.
  • T-score -1.0 to -2.5: Osteopenia.
  • T-score ≤ -2.5: Osteoporosis.
  • T-score ≤ -2.5 with a history of a fragility fracture: Severe (established) osteoporosis.

Pharmacological Therapy (Bisphosphonates)

Bisphosphonates are pyrophosphate analogs that bind to hydroxyapatite crystals in bone and inhibit osteoclast-mediated bone resorption.

• Agents: Oral alendronate (70 mg weekly) or risedronate (35 mg weekly) are first-line. Intravenous zoledronic acid (5 mg annually) is used for patients with gastrointestinal contraindications or compliance issues.
• Crucial Patient Education (Oral Administration):
  1. Take the medication first thing in the morning on an empty stomach.
  2. Take with a full glass (8 oz / 240 mL) of plain water only.
  3. Do not eat, drink, or take other medications for at least 30 minutes after ingestion to ensure absorption.
  4. Remain completely upright (standing or sitting) for at least 30 minutes after taking the pill to prevent chemical esophagitis and esophageal stricture.
• Rare Long-term Complications:
  • Osteonecrosis of the Jaw (ONJ): Usually associated with invasive dental procedures. A dental exam is recommended before starting therapy, and invasive procedures should be completed before initiation.
  • Atypical Femur Fractures (AFF): Subtrochanteric fractures that present with prodromal groin or thigh pain. This risk warrants a "drug holiday" after 3-5 years of continuous use in moderate-risk patients.

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4. Rheumatoid Arthritis (RA) Basics

Rheumatoid Arthritis is a chronic, systemic autoimmune inflammatory disease characterized by symmetric polyarthritis, primarily affecting the small joints of the hands and feet.

Pathophysiology and Clinical Features

Autoantibodies (Rheumatoid Factor and anti-CCP) trigger a chronic inflammatory cascade in the synovium, leading to synovial hypertrophy and the formation of a pannus (granulation tissue). The pannus invades and erodes local cartilage and bone.

• Joint Symptoms: Symmetric joint pain and swelling, with morning stiffness lasting longer than 60 minutes, which characteristically improves with physical activity.
• Joints Affected: PIP, MCP, wrists, and MTP joints. The DIP joints are characteristically spared (unlike OA).
• Diagnostic Markers:
  • Rheumatoid Factor (RF): Moderately sensitive, but lacks specificity (can be positive in other autoimmune diseases and infections).
  • Anti-Cyclic Citrullinated Peptide (anti-CCP) Antibodies: Highly specific (>95%) and a strong predictor of progressive, erosive joint damage.
  • Inflammatory Markers: ESR and CRP are typically elevated.

Disease-Modifying Antirheumatic Drugs (DMARDs)

Early initiation of DMARDs (within 3 months of symptom onset) is critical to prevent irreversible joint destruction.

• First-line DMARD: Methotrexate (dosed weekly, never daily).
  • Co-therapy: Folic acid (1-5 mg daily, omitted on the day of methotrexate) must be co-prescribed to reduce mucosal ulcers, gastrointestinal side effects, and hepatotoxicity.
  • Monitoring: Baseline and periodic CBC (risk of myelosuppression), LFTs (hepatotoxicity), and serum creatinine.
  • Teratogenicity: Highly teratogenic. Effective contraception must be used by both male and female patients during therapy.
• Other DMARDs:
  • Sulfasalazine: Can cause myelosuppression.
  • Leflunomide: Teratogenic.
  • Hydroxychloroquine: Safe in pregnancy. Requires a baseline and annual ophthalmological exam after 5 years of use due to the risk of irreversible macular retinopathy.
• Biologic DMARDs: TNF-alpha inhibitors (e.g., adalimumab, etanercept, infliximab) are added if synthetic DMARDs fail.
  • Screening: Prior to initiating any biologic, patients MUST be screened for latent tuberculosis (via Interferon-Gamma Release Assay [IGRA] or Tuberculin Skin Test [TST]) and viral hepatitis (HBV and HCV), as TNF inhibitors can cause reactivation of these latent infections.