What is the most likely cause of constant, burning pain at a cancer site in the neck that worsens with movement and light touch in a patient with a history of cancer?

Most Likely Diagnosis: Central Sensitization

The clinical presentation described—constant burning pain at the cancer site, exacerbated by movement and light touch (allodynia), spreading along the neck—is most consistent with central sensitization, representing a neuropathic pain syndrome related to cancer and its treatment. 1, 2

Pain Classification Framework

The pain characteristics must be analyzed through established cancer pain pathophysiology:

Neuropathic Pain Features Present

• Burning quality: This is a hallmark descriptor of neuropathic pain caused by nervous system damage, not typical of nociceptive pain 1
• Allodynia (pain with light touch): This hypersensitivity symptom indicates nerve dysfunction and is pathognomonic for neuropathic pain mechanisms 2, 3
• Spreading pattern along anatomical distribution: Pain extending along the neck suggests neural pathway involvement rather than localized tissue damage 2
• Constant nature: While both nociceptive and neuropathic pain can be constant, the combination with burning and allodynia points to neuropathic mechanisms 3

Why Central Sensitization is Most Likely

Central sensitization represents amplified pain processing in the central nervous system following peripheral nerve injury from cancer infiltration or treatment. 2 This mechanism explains:

• The persistent burning quality despite potentially stable tumor burden 2
• Allodynia developing as central neurons become hyperexcitable 2
• Pain spreading beyond the original cancer site as central processing becomes dysregulated 2
• Movement exacerbation due to heightened central pain amplification 1

Ruling Out Alternative Diagnoses

Cervical Dystonia (Least Likely)

• Cervical dystonia is a movement disorder characterized by involuntary muscle contractions causing abnormal neck postures, not a pain syndrome [@general medical knowledge]
• The absence of described abnormal posturing or involuntary movements makes this diagnosis inappropriate [@general medical knowledge]
• Pain in dystonia, when present, is musculoskeletal and cramping, not burning with allodynia [@general medical knowledge]

Opioid Neurotoxicity (Possible but Less Likely)

• While opioid-induced hyperalgesia can cause paradoxical pain sensitization, this typically presents as diffuse pain worsening despite dose escalation [@general medical knowledge]
• The localized nature at the cancer site and specific anatomical spread pattern is more consistent with structural nerve damage than opioid neurotoxicity 2
• No information provided about opioid dosing or escalation patterns that would support this diagnosis [@general medical knowledge]

Trigeminal Neuralgia (Unlikely)

• Trigeminal neuralgia causes paroxysmal, electric shock-like facial pain in trigeminal nerve distributions (V1, V2, V3) [@general medical knowledge]
• The described pain is constant, not paroxysmal, which contradicts classic trigeminal neuralgia [@general medical knowledge]
• Pain spreading "along the neck" does not follow trigeminal distribution patterns [@general medical knowledge]
• Trigeminal neuralgia typically has trigger zones but is not described as burning or constant [@general medical knowledge]

Clinical Implications for Management

Assessment Priorities

• Comprehensive evaluation must distinguish neuropathic from nociceptive components, as they require different therapeutic approaches [@2@, @3@]
• Physical examination should specifically test for allodynia, hyperalgesia, and hyperpathia to confirm neuropathic pain [@3@]
• Imaging and clinical assessment should evaluate for tumor progression causing nerve compression or infiltration 1

Treatment Approach

• Neuropathic cancer pain typically does not respond adequately to opioids alone [@8@]
• Management requires adjuvant medications including antidepressants, anticonvulsants, and anti-arrhythmic agents 2
• Combined pharmacotherapy targeting both nociceptive and neuropathic mechanisms is often necessary, as head and neck cancer patients commonly experience both pain types simultaneously [@10@]

Critical Pitfalls to Avoid

• Do not treat with opioids alone: Neuropathic pain mechanisms require adjuvant agents for adequate control 2
• Do not dismiss allodynia: Light touch hypersensitivity is a red flag for neuropathic pain requiring specific management 2, 3
• Do not delay assessment for tumor progression: New or worsening pain may indicate disease advancement requiring oncologic intervention beyond analgesia [@2@, @3@]
• Do not confuse constant pain with nociceptive pain: The burning quality and allodynia override the constant nature in determining neuropathic etiology [@2@, @8