What is the management plan for a 28-year-old female with slight back pain, bilateral posterior thigh and calf pain, elevated Creatine Kinase (CK) level, and normal Magnetic Resonance Imaging (MRI) of the lumbar spine?

Management of Bilateral Posterior Leg Pain with Mildly Elevated CK

This presentation requires a systematic workup for myositis and other neuromuscular conditions, with initial conservative management including NSAIDs for symptom relief, while monitoring for progression that would indicate more serious muscle disease.

Initial Diagnostic Workup

The mildly elevated CK (206 U/L, just above normal <180 U/L) with bilateral posterior thigh and calf pain requires comprehensive evaluation to distinguish between benign causes and inflammatory muscle disease:

Essential Laboratory Tests

• Complete muscle enzyme panel: Check aldolase, AST, ALT, and LDH, as these can be elevated alongside CK in myositis 1
• Inflammatory markers: ESR and CRP to assess for systemic inflammation 1
• Troponin level: Essential to evaluate for myocardial involvement, which can occur with myositis 1
• Autoimmune panel: ANA, RF, anti-CCP, and consider paraneoplastic autoantibody testing for myositis 1
• Comprehensive metabolic panel: To assess renal and liver function 2

Clinical Assessment Priorities

• Evaluate for true muscle weakness (not just pain): Muscle weakness is more typical of myositis than pain alone 1
• Assess proximal muscle strength: Test shoulder abduction, hip flexion, and ability to rise from chair without using arms 2
• Screen for red flag symptoms: Progressive weakness, dysphagia, dysarthria, dysphonia, or dyspnea require urgent evaluation 2
• Medication review: Assess for statins or other drugs that can cause CK elevation 1, 2

Management Based on Current Presentation

Grade 1 (Mild) Symptoms - Current Status

Given the patient has only slight back pain and bilateral leg pain without documented weakness, this appears to be Grade 1 severity:

• Continue monitoring without immunosuppression at this stage 1
• Initiate symptomatic treatment: Acetaminophen or NSAIDs for pain relief if no contraindications 1, 2
• Repeat CK in 1-2 weeks: Monitor for progression or resolution 2
• Advise rest from strenuous activity: Avoid exercise that could transiently elevate CK 1, 2

If CK Rises to ≥3× ULN (≥540 U/L)

Should repeat testing show CK elevation ≥3× upper limit of normal with persistent symptoms:

• Initiate prednisone 0.5-1 mg/kg daily 1
• Refer to rheumatology or neurology for further evaluation 1
• Consider EMG and MRI of affected muscles if diagnosis remains uncertain 1
• Consider muscle biopsy if diagnosis is uncertain and overlap with neurologic syndromes is suspected 1

Differential Diagnosis Considerations

Polymyalgia Rheumatica (PMR)

The bilateral posterior thigh and calf pain with slight back pain could represent PMR, which presents with:

• Acute, predominantly bilateral shoulder and/or hip pain with morning stiffness 1
• Key distinction: PMR typically has normal CK levels, making this diagnosis less likely 1
• If PMR is suspected, prednisone 10-20 mg/day is appropriate for Grade 2 symptoms 1

Other Causes to Exclude

• Post-viral myositis: Less likely without URI symptoms but not excluded 2
• Medication-induced myopathy: Critical to review all medications, particularly statins 1, 2
• Exercise-induced CK elevation: Can occur with eccentric exercise, but typically resolves within 1-2 weeks 1, 2
• Idiopathic hyperCKemia: Approximately 25% of cases remain undiagnosed after comprehensive workup 3

Monitoring Strategy

Short-term (1-4 weeks)

• Repeat CK, ESR, CRP in 1-2 weeks 1, 2
• Reassess for development of weakness: Progressive weakness requires urgent re-evaluation 2
• Expected course: Mild CK elevation should resolve spontaneously within 1-2 weeks with rest and conservative management 2

Indications for Urgent Escalation

• CK >10× ULN (>1800 U/L): Stop any causative medications, consider hospitalization, check renal function 1
• Development of true muscle weakness: Particularly proximal muscle groups 2
• Any red flag symptoms: Dysphagia, dysarthria, dysphonia, dyspnea, or signs of myocardial involvement 2

If Symptoms Persist Beyond 4 Weeks

• Persistent elevation beyond 4 weeks or development of weakness warrants comprehensive neuromuscular evaluation 2
• Consider EMG, muscle MRI, and possible muscle biopsy 1
• Formal rheumatology or neurology consultation 1

Important Clinical Caveats

The normal lumbar spine MRI effectively rules out structural spinal pathology but does not exclude inflammatory muscle disease, which requires muscle-specific imaging if suspected 1. The key distinction is that muscle weakness (not pain) is the hallmark of myositis 1, so careful strength testing is essential. Many patients with mild hyperCKemia will not develop significant muscle disease on longitudinal follow-up 3, but vigilant monitoring for progression remains critical to avoid missing treatable inflammatory conditions.