What is the likely cause and first-line treatment for a painful shoulder spasm radiating down the arm to the forearm?

Shoulder Spasm with Radiating Forearm Pain

For painful shoulder spasms radiating to the forearm, initiate treatment with gentle stretching and mobilization techniques focusing on external rotation and abduction, combined with NSAIDs (ibuprofen preferred over acetaminophen), and consider adding a short course of a muscle relaxant like cyclobenzaprine for acute spasm relief. 1, 2, 3, 4

Most Likely Causes

The clinical presentation suggests one of three primary etiologies:

• Cervical radiculopathy - nerve root compression causing radiating pain below the elbow with possible motor/sensory changes 5, 6
• Shoulder impingement syndrome with secondary brachioradialis muscle involvement - subacromial pathology causing referred pain through the forearm 2, 7
• Cervical dystonia/muscle spasm - painful dystonic spasms of cervical muscles radiating distally 1

Critical distinguishing feature: Radiating pain accompanied by motor or sensory changes, particularly below the elbow, strongly suggests neurologic etiology rather than primary shoulder pathology 8, 9

First-Line Treatment Algorithm (Weeks 0-3)

Immediate Interventions

• Start gentle passive and active-assisted range of motion exercises within pain-free ranges, specifically targeting external rotation and abduction movements 1, 2, 3
• Prescribe ibuprofen (taken before bedtime for sleep improvement) - superior to acetaminophen for rotator cuff-related pain 1, 3
• Add cyclobenzaprine as adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions - use only for short periods (2-3 weeks maximum) 4
• Apply ice before each exercise session for symptomatic relief 3

Positioning and Protection

• Never allow sleeping on the affected shoulder - proper positioning during sleep is crucial 3
• Educate on correct arm positioning and handling to prevent further injury 2
• Avoid static positioning or strapping of the upper extremity 3

Progressive Treatment (Weeks 3-8)

• Advance active range of motion gradually while restoring proper shoulder alignment and strengthening weak muscles in the shoulder girdle 1, 2, 3
• Progress to intensive strengthening exercises targeting rotator cuff and scapular stabilizers 2, 3
• Emphasize posterior shoulder musculature strengthening to counterbalance anterior muscles 2
• Address scapular dyskinesis through specific exercises if present 2, 3

Adjunctive Interventions

For Persistent Pain Despite Conservative Management

• Subacromial corticosteroid injection when pain is clearly related to rotator cuff or bursa inflammation 1, 3
• Nerve-stabilizing agents (pregabalin, gabapentin, or duloxetine) if neuropathic component suspected 1
• Botulinum toxin type A injections into affected muscles for pain management and spasm control if cervical dystonia confirmed 1

When to Consider Specialist Referral

• Refer to rehabilitation specialist if cervical dystonia, neuropathy, or significant shoulder dysfunction identified 1
• Obtain MRI or ultrasound if no improvement after 3-4 weeks of conservative management 3
• Consider orthopedic evaluation for possible labral pathology if instability symptoms persist 2

Critical Pitfalls to Avoid

• Do not overlook cervical spine pathology - cervical spondylosis causes radiating arm/forearm pain that mimics rotator cuff pathology 9
• Early mobilization is mandatory to prevent adhesive capsulitis (frozen shoulder) 3
• Do not miss brachioradialis muscle pain - common in patients with subacromial impingement syndrome, causing sharp shooting pain during activity and aching at rest through forearm, back of hand, thumb and index finger 7
• Assess for neurologic deficits - diminished deep tendon reflexes (particularly triceps) are the most common neurologic finding in cervical radiculopathy 5
• Perform Spurling test to confirm cervical radiculopathy if suspected 5

Reassessment Timeline

• If no improvement after 3-4 weeks of conservative management, obtain imaging (MRI preferred) and consider specialist referral 3, 5
• Ensure complete resolution of symptoms before returning to full overhead activities 2, 3
• Red flag symptoms (progressive neurologic deficit, severe unrelenting pain, signs of myelopathy) require immediate imaging and specialist evaluation 5, 6