How is trapezius spasticity diagnosed?

Diagnosing Trapezius Spasticity

Trapezius spasticity is diagnosed through clinical examination demonstrating velocity-dependent resistance to passive stretch of the trapezius muscle, combined with electrodiagnostic testing to confirm upper motor neuron pathology and exclude nerve injury.

Clinical Examination Findings

Essential Physical Examination Components

• Assess for velocity-dependent hyperactivity of stretch reflexes in the trapezius muscle during passive movement, which is the defining characteristic of spasticity 1
• Evaluate muscle tone by passively moving the shoulder through range of motion at varying speeds—spasticity increases with faster movement velocity 1
• Observe for associated upper motor neuron signs including hyperreflexia, clonus, and pathological reflexes, as spasticity is only one component of upper motor neuron syndrome 1
• Document shoulder position and scapular alignment to differentiate spasticity from trapezius palsy, which presents with shoulder drooping and lateral scapular translation 2

Critical Differentiation from Trapezius Palsy

• Perform the Active Elevation Lag Sign: patients with trapezius palsy demonstrate active forward elevation lag with compensatory spinal hyperextension, which is absent in spasticity (100% sensitivity, 95% specificity) 3
• Assess the Triangle Sign in prone position: this sign appears in trapezius dysfunction from nerve palsy but not in spasticity 3
• Examine for scapular winging pattern: trapezius palsy causes lateral translation and downward rotation of the scapula, whereas spasticity causes increased muscle tone without this deformity 2

Electrodiagnostic Testing

Nerve Conduction Studies

• Measure spinal accessory nerve latency to middle trapezius (normal: 3.0 ± 0.2 msec) and lower trapezius (normal: 4.6 ± 0.3 msec) to exclude nerve injury as the cause of dysfunction 4
• Perform complete electrodiagnostic examination to differentiate between upper motor neuron spasticity and lower motor neuron trapezius palsy 2
• Use clinical neurophysiologic recordings of reflex activity to differentiate among various types of spasticity and objectively measure treatment response 1

Underlying Etiology Assessment

Identify the Upper Motor Neuron Lesion

• Obtain brain and spinal cord MRI emergently if spasticity represents new or acute neurological deterioration to exclude stroke, hemorrhage, or spinal cord compression 5
• Review patient history for established neurological conditions such as cerebral palsy (where spasticity affects 85-91% of patients), stroke, or spinal cord injury 6
• Recognize that spasticity reflects increased excitatory state at the segmental spinal level from upper motor neuron lesions, not increased muscle spindle sensitivity 1

Modified Ashworth Scale Assessment

• Grade spasticity using the Modified Ashworth Scale during passive movement of the trapezius to quantify severity and track treatment response 7
• Document baseline spasticity measurements before initiating any intervention to allow objective comparison 7

Associated Findings to Document

• Assess pressure pain thresholds over the trapezius and surrounding muscles, as spasticity often involves altered pain sensitivity 7
• Measure shoulder range of motion in all planes, particularly abduction, flexion, and external rotation, which are commonly limited by trapezius spasticity 7
• Evaluate for functional disability including paresis, fatigability, and lack of dexterity, which account for most patient complaints beyond spasticity itself 1

Critical Pitfalls to Avoid

• Never assume chronic spasticity suddenly worsens without cause—investigate for acute pathology including UTI, constipation, or new neurological injury, as established spasticity does not spontaneously deteriorate 5
• Do not confuse spasticity with rigidity or contracture—spasticity is velocity-dependent and improves with slow passive movement, whereas rigidity is constant and contractures represent fixed structural changes 1
• Avoid attributing all trapezius dysfunction to spasticity—always exclude spinal accessory nerve injury through electrodiagnostic testing, especially with history of posterior cervical triangle surgery 2, 4