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Case History

Image not available. You are reviewing a 48-year-old woman with recurrent breast cancer following a right-sided mastectomy and chemotherapy she received five years ago. This patient is a candidate for further treatment of ipsilateral supraclavicular nodal and lung involvement. She describes a one-week history of right arm pain and weakness, with constant burning along the medial aspect of the whole limb. She reports a slight reduction in pain with 240 mg of oral codeine phosphate daily. You elicit reduced grip strength and altered sensation in C8-T1 dermatomes.

What is your approach to diagnosis of pain in this patient?

How would you manage this patient's pain?

Background

What is your approach to diagnosis of pain in this patient?

Image not available. Neuropathic pain should be suspected when a patient describes specific pain qualities in an area of altered sensation consistent with a neuroanatomical distribution.1 Suggestive descriptors that correlate strongly with altered sensation include 'burning', 'stinging' and 'shooting'.2

Neuropathic pain arises as a result of a lesion or disease affecting the central or peripheral somatosensory system.3 The term encompasses heterogeneous syndromes with diverse aetiologies.4 The underlying mechanisms are incompletely understood and include: peripheral and central sensitization, neuronal hyperexcitability, maintained sympathetic activity, dysfunctional central inhibition, dorsal horn rewiring, and phenotypic switch.4

The prevalence of cancer patients with neuropathic pain ranges between 19% and 39%, with 19%-24% of all pains having a neuropathic mechanism.5 Cancer pain typically arises from mixed nociceptive and neuropathic mechanisms, with pain considered more or less neuropathic.6,7 Failure to identify a neuropathic component may contribute to the under-treatment of pain.5

Approximately two-thirds of neuropathic cancer pain arises from the cancer itself, through direct invasion or paraneoplastic neuropathy, with 20% arising from anticancer treatment. Up to 10% reflects comorbidity.5 In the absence of previous radiotherapy, brachial plexopathy secondary to metastatic involvement is likely in this case.

Patients may describe or exhibit the following:1,8

  • pain occurring without a precipitating trigger (spontaneous pain), like shooting electrical attacks (paroxysmal pain)

  • numbness or reduced sensation to painful (hypoalgesia) and non-painful stimuli (hypoaesthesia)

  • unusual and unpleasant sensations, such as tingling or pins and needles (dysaesthesia/paraesthesia)

  • pain responses to usually non-painful stimuli (allodynia)

  • exaggerated response to usually painful stimuli (hyperalgesia)

  • abnormal thermal sensation.

Clinical examination focuses on identifying abnormal sensation in the area of pain. Allodynia is demonstrated by eliciting pain through gentle brushing (normally non-painful). Response to pin-prick testing may be reduced (numbness) or exaggerated (hyperalgesia). Temporal summation, in which there is increasing pain sensation with repetitive application of identical stimuli, is demonstrated by repeated pin-pricks with intervals of under 3 seconds for 30 seconds.1,8

Although assessment tools exist there are no universally accepted and validated diagnostic criteria for neuropathic cancer pain.1,...

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