What are the differential diagnoses and management options for chronic shoulder pain radiating to the arm in a patient with no history of trauma, who recently started taking pregabalin (lyrica) a few weeks ago?

Differential Diagnoses for Chronic Shoulder Pain Radiating to the Arm Without Trauma

The most likely differential diagnoses in this clinical scenario are cervical radiculopathy, rotator cuff pathology (particularly in patients over 35-40 years), and peripheral neuropathy, with the recent pregabalin initiation being coincidental rather than causative. 1

Primary Differential Diagnoses

Cervical Radiculopathy (Most Likely)

• Chronic shoulder pain radiating down the arm without trauma strongly suggests cervical spine pathology with nerve root compression. 1
• Key features include numbness, tingling, weakness, or radiation of pain down the arm, which are hallmark symptoms of cervical radiculopathy. 1
• Pain originating from the scapular region frequently indicates referred pain from the cervical spine rather than primary shoulder pathology. 1

Rotator Cuff Disease (Age-Dependent)

• In patients over 35-40 years, rotator cuff disease and degenerative changes are predominant causes of chronic shoulder pain. 1, 2
• Anterior shoulder pain specifically suggests rotator cuff or biceps tendon pathology. 1
• Most rotator cuff pathology can initially be managed conservatively without surgical intervention. 2

Peripheral Neuropathy

• Chronic neuropathic pain conditions can present as shoulder and arm pain with radiation. 3
• Associated symptoms include burning, aching sensations, allodynia, and sensory changes. 3

Critical Assessment Points

Pain Location Mapping

• Anterior shoulder pain: rotator cuff or biceps pathology 1
• Superior shoulder pain: acromioclavicular joint disease 1
• Scapular region pain: cervical spine referred pain or rotator cuff pathology 1

Age-Specific Considerations

• Patients over 35-40 years: prioritize rotator cuff disease, degenerative changes, and cervical spine pathology 1, 2
• Patients under 35 years: consider instability, labral tears, though less likely without trauma history 1

Pregabalin Relationship Analysis

Pregabalin as Causative Agent: Unlikely

• Pregabalin does not cause shoulder pain as a recognized adverse effect. 4, 5
• The temporal relationship (pain starting with pregabalin initiation) is likely coincidental rather than causative.
• Common pregabalin adverse effects include somnolence (15-25%) and dizziness (27-46%), not musculoskeletal pain. 4, 5

Pregabalin as Treatment Consideration

• If neuropathic pain is confirmed (cervical radiculopathy or peripheral neuropathy), pregabalin may actually be therapeutic rather than causative. 3
• Gabapentin is recommended as first-line oral pharmacological treatment for chronic neuropathic pain, with pregabalin as an alternative if inadequate response. 3
• For post-herpetic neuralgia specifically, pregabalin shows efficacy with NNT of 4.93. 3

Diagnostic Algorithm

Initial Clinical Assessment

1. Document exact pain location and radiation pattern to distinguish shoulder pathology from cervical radiculopathy 1
2. Assess for neurological symptoms: numbness, tingling, weakness in specific dermatomal distributions 1
3. Test for regional sensory changes, allodynia, or hyperpathia suggesting neuropathic pain component 3
4. Evaluate shoulder range of motion, strength, and impingement signs 3

Imaging Strategy

• Cervical spine imaging is warranted given radiation to arm without trauma history 1
• Shoulder radiographs (minimum three views: AP internal rotation, AP external rotation, and axillary or scapula-Y view) if shoulder pathology suspected 2
• MRI without contrast for soft tissue evaluation if rotator cuff or labral pathology suspected 2

Management Approach

If Cervical Radiculopathy Confirmed

• Continue pregabalin as it may provide therapeutic benefit for neuropathic pain. 3
• Typical adult pregabalin regimen: titrate to 300-600 mg daily in divided doses 3
• Gabapentin remains first-line (typical dose 2400 mg/day in divided doses) if pregabalin not yet optimized 3

If Rotator Cuff Pathology Confirmed

• Refer to rehabilitation specialist for comprehensive management 3
• Most rotator cuff pathology can be managed conservatively initially 2
• Pregabalin should be discontinued if no neuropathic component exists, as it provides no benefit for pure musculoskeletal pain 4, 5

If Neuropathic Pain Features Present

• Prescribe nerve-stabilizing agents such as pregabalin, gabapentin, or duloxetine for pain management. 3
• For cervical dystonia or muscle spasms: consider botulinum toxin type A injections into affected muscles 3

Critical Pitfalls to Avoid

• Do not assume pregabalin caused the shoulder pain without evidence of direct causation; temporal association does not equal causation. 4, 5
• Do not miss cervical spine pathology by focusing exclusively on the shoulder when pain radiates to the arm. 1
• Do not discontinue pregabalin prematurely if neuropathic pain component exists, as it may be providing partial benefit. 3
• In elderly patients, do not assume absence of trauma means absence of fracture, as osteoporotic fractures can occur with minimal or unrecognized trauma. 1