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Case History

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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?

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Background

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

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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

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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

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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

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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.

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Patients may describe or exhibit the following:1,8

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  • 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.

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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

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

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