What are the possible causes of acute onset right shoulder pain radiating down the arm with numbness in digits 3-5 after carrying a heavy object in an elderly male patient?

Acute Shoulder Pain with Radicular Symptoms: Differential Diagnosis

The most likely diagnosis in this elderly male is cervical radiculopathy (C8-T1 nerve root compression), given the acute onset with heavy lifting, radiation down the arm, and numbness specifically in digits 3-5 (ulnar distribution), without weakness. 1

Primary Diagnostic Considerations

Cervical Radiculopathy (Most Likely)

• C8-T1 nerve root compression is the leading diagnosis given the specific pattern of numbness in digits 3-5 (ring and small fingers), which follows the ulnar nerve distribution originating from C8-T1 nerve roots 1, 2
• The mechanism of heavy lifting can cause acute cervical disc herniation or exacerbate pre-existing cervical spondylosis, both common causes of radiculopathy in elderly patients 1
• Pain radiating from shoulder down the arm with sensory changes but preserved motor function is classic for radiculopathy in the acute phase 1
• The absence of weakness does not exclude radiculopathy, as sensory symptoms often precede motor deficits 1

Brachial Plexopathy - Lower Trunk Injury

• Lower brachial plexus injury (C8-T1 roots) can present identically with shoulder pain radiating down the arm and numbness in ulnar distribution 2
• Traction injury from carrying heavy objects can stretch the lower trunk of the brachial plexus 2
• Post-operative C8-T1 nerve palsies present with weakness of intrinsic hand muscles and sensory symptoms in ulnar two digits, though this patient has no surgical history 2

Parsonage-Turner Syndrome (Neuralgic Amyotrophy)

• PTS typically presents with severe acute shoulder pain followed by progressive weakness of shoulder girdle and upper arm musculature 3
• The syndrome is difficult to diagnose as it mimics cervical radiculopathy 3
• Key distinguishing feature: PTS presents with delayed neurological deficits (days to weeks) after pain onset, whereas this patient has concurrent symptoms 2, 3
• PTS more commonly affects upper brachial plexus (C5-C6) rather than lower trunk 3, 4

Less Likely But Important Differential Diagnoses

Dropped Shoulder Syndrome

• Can cause lower cervical radiculopathy through muscle spasm compressing cervical roots 5
• More common in younger patients (mean age 36.7 years) and predominantly affects women (4:1 female:male ratio) 5
• Typically presents with visually detectable dropped shoulder and involves C7-T1 roots 5

Rotator Cuff Pathology

• In patients over 35-40 years, rotator cuff disease is a predominant cause of shoulder pain 6, 7
• However, rotator cuff tears typically do not cause numbness in specific digits 8
• The neurological symptoms (numbness digits 3-5) make this diagnosis unlikely as the primary pathology 6

Vascular Compromise

• Axillary artery injury is more likely with proximal humeral fractures, open fractures, or shoulder dislocation 8
• The absence of these findings and presence of neurological rather than vascular symptoms makes this unlikely 8

Critical Diagnostic Algorithm

Immediate Assessment Required

1. Perform detailed neurological examination focusing on:

   • C8-T1 dermatome sensation (medial forearm, ulnar two digits) 2
   • Intrinsic hand muscle strength (interossei, lumbricals) 2
   • Grip strength and finger abduction/adduction 2

2. Assess for red flag symptoms:

   • Progressive motor weakness suggests urgent nerve compression 1
   • Bilateral symptoms or myelopathic signs require immediate imaging 1
   • Horner's syndrome (miosis, ptosis, anhydrosis) suggests sympathetic chain involvement at T1 level 2

Imaging Strategy

• Initial imaging: Cervical spine radiographs to assess alignment and degenerative changes 8
• MRI cervical spine without contrast is the definitive study to identify disc herniation, foraminal stenosis, or nerve root compression 1, 4
• MRI of the brachial plexus (MR neurography) can show high signal intensity in affected nerve roots, though this finding is not specific and can occur in both radiculopathy and neuralgic amyotrophy 4

Common Diagnostic Pitfalls

• Do not assume absence of weakness excludes significant nerve pathology - sensory symptoms often precede motor deficits in radiculopathy 1
• Do not confuse ulnar nerve entrapment at the elbow with C8-T1 radiculopathy - cervical radiculopathy causes shoulder pain with radiation, while ulnar neuropathy typically spares the shoulder 1
• Do not miss Parsonage-Turner syndrome by assuming all shoulder pain with neurological symptoms is radiculopathy - PTS requires different management (conservative vs. potential surgical decompression for radiculopathy) 3
• High signal intensity on MR neurography of brachial plexus is not specific for neuralgic amyotrophy and can be seen in C5-C6 radiculopathy as well 4

Time-Sensitive Considerations

• If Parsonage-Turner syndrome is suspected, monitor closely for delayed progressive weakness which typically develops days after pain onset 2, 3
• Massive nerve compression with progressive motor deficits requires urgent surgical evaluation, similar to massive rotator cuff tears requiring expedited repair 8