What is the appropriate workup for a patient presenting with weakness?

Comprehensive Workup for Patients Presenting with Weakness

The initial workup for a patient with muscle weakness should include comprehensive laboratory testing, electrophysiological studies, and imaging to distinguish true muscle weakness from pain-related limitation of movement and document the pattern of weakness (proximal vs. distal). 1

Step 1: Distinguish True Weakness from Other Symptoms

• Determine if the patient has true muscle weakness (loss of power resulting in reduction of motor function) versus fatigue, pain-limited movement, or generalized malaise 2
• Document pattern of weakness: proximal vs. distal, symmetric vs. asymmetric, focal vs. generalized 1
• Assess onset (acute vs. chronic) and progression (stable vs. worsening) 3

Step 2: Laboratory Testing

Basic Laboratory Panel:

• Complete blood count
• Comprehensive metabolic panel
• Inflammatory markers (ESR, CRP) 4, 1

Muscle Inflammation Assessment:

• Creatine kinase (CK)
• Transaminases (AST, ALT)
• Lactate dehydrogenase (LDH)
• Aldolase 4, 1

Endocrine and Metabolic Workup:

• Thyroid function tests
• 25-OH vitamin D level
• Calcium and parathyroid hormone
• Glucose/HbA1c 1

Cardiac Assessment:

• Troponin
• ECG (to evaluate myocardial involvement) 4, 1

Step 3: Autoimmune and Specialized Testing

Autoimmune Testing:

• ANA, RF, anti-CCP antibodies
• Autoimmune myositis panel 4, 1

Neurologic Testing:

• Acetylcholine receptor (AChR) antibodies
• Anti-striated muscle antibodies
• MuSK and LPR4 antibodies (if AChR negative)
• Paraneoplastic autoantibody panel 4, 1

Step 4: Electrophysiological Studies and Imaging

Electrophysiological Studies:

• Electromyography (EMG)
• Nerve conduction studies (NCS)
• Neuromuscular junction testing with repetitive stimulation 4, 1

Imaging:

• MRI of affected limbs (to evaluate muscle damage and inflammation)
• MRI of brain and/or spine (depending on symptoms) 4, 1

Step 5: Advanced Diagnostic Testing

Consider Based on Initial Results:

• Lumbar puncture (if Guillain-Barré syndrome suspected)
• Muscle biopsy (if diagnosis uncertain after initial workup)
• Pulmonary function testing (NIF/VC) if respiratory involvement suspected 4

Specialist Referral Guidelines

Urgent Referral (Same Day):

• Rapidly progressive weakness
• Respiratory or cardiac involvement
• Dysphagia
• Severe weakness limiting self-care 4, 1

Early Referral:

• Uncertain diagnosis after initial workup
• Moderate to severe weakness
• Progressive symptoms
• Presence of systemic symptoms 1

Common Pitfalls to Avoid

• Failing to distinguish true weakness from pain-related limitation of movement
• Missing cardiac involvement which can be life-threatening
• Overlooking common causes (medication side effects, electrolyte abnormalities)
• Delaying specialist referral for rapidly progressive weakness
• Initiating immunosuppressive therapy without ruling out infectious causes 1

Remember that weakness can be a manifestation of serious neurological, rheumatological, endocrine, or metabolic disorders, and early identification of the underlying cause is crucial for appropriate management and improved outcomes.