What are the differential diagnosis options for an adult patient presenting with right-sided neuropathic skin pain in the area of the acromion process and below the clavicle?

Differential Diagnosis for Right-Sided Neuropathic Skin Pain in the Acromion and Infraclavicular Region

The most likely diagnosis is cervical radiculopathy with nerve root compression, particularly affecting C4-C5 nerve roots, which innervate the skin over the acromion and infraclavicular region. 1

Primary Differential Diagnoses

Cervical Radiculopathy (Most Likely)

• Chronic shoulder pain with neuropathic characteristics strongly suggests cervical spine pathology with nerve root compression, particularly when pain is described as burning, with numbness, tingling, or allodynia in the distribution of the acromion and infraclavicular area 1
• C4 nerve root compression produces pain and sensory changes over the superior shoulder and acromion process 1
• C5 nerve root involvement causes pain radiating to the lateral shoulder and upper arm region 1
• The neuropathic quality (skin pain, burning, allodynia) is a hallmark feature distinguishing radiculopathy from pure musculoskeletal pathology 2, 1

Hemiplegic Shoulder Pain with Neuropathic Features

• If the patient has a history of stroke, central poststroke pain or hemiplegic shoulder pain must be considered 2
• Testing for regional sensory changes, allodynia, or hyperpathia in the shoulder region confirms neuropathic pain component 2
• Central poststroke pain typically presents as burning or aching with allodynia associated with touch, cold, or movement 2

Peripheral Nerve Entrapment Syndromes

• Suprascapular nerve entrapment can cause neuropathic pain in the posterior and superior shoulder region, though less commonly affects the anterior infraclavicular area 2
• Supraclavicular nerve injury or entrapment produces burning pain and dysesthesias over the clavicle and upper chest wall 3

Rotator Cuff Disease with Secondary Neuropathic Pain

• Approximately 20% of patients with chronic shoulder pain develop a neuropathic pain component, with an additional 19% having possible neuropathic features 4
• Patients with neuropathic shoulder pain have significantly higher pain scores and longer symptom duration compared to pure nociceptive pain 4, 5
• The Shoulder Pain and Disability Index (SPADI) score can serve as an independent prognostic factor for neuropathic pain development (odds ratio = 1.189) 5

Neuropathic Arthropathy (Charcot Shoulder)

• Consider in patients with syringomyelia, diabetes, chronic alcoholism, or leprosy 6
• Presents with swelling, paresthesia or hypoesthesia (76% of cases), and reduced range of motion (90% of cases) 6
• Pain is present in only 53% of cases, making the diagnosis challenging 6

Critical Diagnostic Approach

Clinical Evaluation

• Document exact pain location and radiation pattern to distinguish shoulder pathology from cervical radiculopathy 1
• Assess for neurological symptoms including numbness, tingling, weakness in specific dermatomal distributions 1, 7
• Test for regional sensory changes, allodynia (pain from non-painful stimuli), or hyperpathia (exaggerated pain response) 2, 3
• Evaluate sensitivity to pinprick, touch, pressure, cold, heat, and vibration in the affected area 3
• Assess for spontaneous pain (continuous or intermittent) and pain evoked by daily activities 3

Imaging Protocol

• MRI of the cervical spine without contrast is the preferred initial advanced imaging when clinical examination supports radiculopathy, as it directly visualizes disc herniations, osteophytes, and nerve root compression 1
• Plain radiographs of the cervical spine should be obtained first to assess for gross structural abnormalities and degenerative changes 1
• Shoulder MRI is recommended only if physical examination suggests concurrent rotator cuff pathology 1
• Do not assume neuropathic pain is simply "muscle tension" without ruling out structural cervical spine pathology 1

Electrodiagnostic Testing

• Consider electrodiagnostic testing if imaging is negative or equivocal, with sensitivity over 80% and specificity of 95% for confirming nerve compression 1

Management Algorithm

If Cervical Radiculopathy is Confirmed

First-Line Pharmacotherapy:

• Tricyclic antidepressants (amitriptyline 75 mg at bedtime) have been shown to lower daily pain ratings and improve global functioning 2
• Anticonvulsants are reasonable as first-line treatment: gabapentin or pregabalin 300-600 mg daily in divided doses 2, 1
• Lamotrigine can reduce daily pain ratings, though only 44% of patients have good clinical response 2

Second-Line Options:

• Carbamazepine or phenytoin, though usefulness is not well established 2
• Topical lidocaine for localized neuropathic pain 2

If Rotator Cuff Pathology with Neuropathic Features

• Neuropathic pain should be assessed when prescribing treatment programs in all patients with shoulder pain 4
• Complete rest from aggravating activities until asymptomatic 7
• Physical therapy focusing on range of motion, scapular stabilization, and rotator cuff strengthening 7, 8
• Avoid overhead pulley exercises, which can worsen rotator cuff pathology 7, 8
• Consider neuromodulating pain medications (pregabalin, gabapentin, or duloxetine) for the neuropathic component 1

If Hemiplegic Shoulder Pain (Post-Stroke)

• A trial of neuromodulating pain medications is reasonable for patients with clinical signs of neuropathic pain 2
• Botulinum toxin injection can reduce severe hypertonicity in hemiplegic shoulder muscles 2
• Suprascapular nerve block may be considered as adjunctive treatment 2

Common Pitfalls to Avoid

• Do not delay cervical spine imaging if red flags are present or if neuropathic features dominate the clinical picture 1
• Do not assume absence of trauma means absence of pathology, especially in elderly patients 7
• Patients may be confused by unusual sensations and unable to effectively describe symptoms, requiring careful questioning about burning, electric, shooting, or skin sensitivity 3
• Do not treat with NSAIDs or physical therapy alone when neuropathic pain features are present, as these patients require nerve-stabilizing medications 1, 4
• The communication barrier regarding unusual neuropathic sensations may contribute to inadequate assessment and delayed diagnosis 3