A 65-year-old woman comes to the office to discuss pain at the posterior chest wall. She was seen 4 months ago for acute shingles involving a right mid-thoracic dermatome. The patient was not treated at that time because she had a delayed presentation and the lesions were already well-crusted and healing. The skin lesions subsequently cleared completely. However, since then, she has had persistent burning and stabbing pain in the same region that has now become severe. She has tried oral acetaminophen without relief. During discussion of treatment options, the patient says she does not want any systemic medications due to concerns about possible side effects. She is started on topical capsaicin cream, and her pain improves markedly over the next several days. Decreased activity of which of the following neurotransmitters is most likely associated with pain relief in this patient?

Question

A 65-year-old woman comes to the office to discuss pain at the posterior chest wall.  She was seen 4 months ago for acute shingles involving a right mid-thoracic dermatome.  The patient was not treated at that time because she had a delayed presentation and the lesions were already well-crusted and healing.  The skin lesions subsequently cleared completely.  However, since then, she has had persistent burning and stabbing pain in the same region that has now become severe.  She has tried oral acetaminophen without relief.  During discussion of treatment options, the patient says she does not want any systemic medications due to concerns about possible side effects.  She is started on topical capsaicin cream, and her pain improves markedly over the next several days.  Decreased activity of which of the following neurotransmitters is most likely associated with pain relief in this patient?

Quizplus · Accepted Answer

11ec160b_3c0c_19eb_9249_3dfdaa2409c2_MD0001_00 Shingles is due to reactivation of latent varicella zoster virus in sensory ganglia. It causes a vesicular rash and acute neuritis due to injury to the nerves. The initial pain fades within a few weeks to months, but a subset of patients will have residual neuropathic pain in the affected dermatome. This pain, termed postherpetic neuralgia (PHN), relates to sensitization of afferent nerves in the dorsal horn. It may last several months or longer, and has a burning, stabbing, or gnawing character. PHN is usually managed with tricyclic antidepressants (eg, amitriptyline) or anticonvulsants (eg, gabapentin, pregabalin), but nonsystemic options for PHN include lidocaine patches or topical capsaicin. Capsaicin is an irritant found in the chili pepper family. It causes excessive activation of TRPV1 (a transmembrane cation channel), causing a buildup of intracellular calcium that results in long-lasting dysfunction of nociceptive nerve fibers (defunctionalization). In addition, capsaicin causes release and subsequent depletion of substance P, a polypeptide neurotransmitter involved in transmission of pain signals. On initial application, topical capsaicin causes burning, stinging, and erythema, but persistent exposure leads to a moderate reduction in pain over time. (Choices A, D, E, and G) Capsaicin does not achieve its analgesic effect by acting on these neurotransmitters. (Choices B and C) Endorphins and dynorphins are endogenous opioid peptides that achieve their pain-relieving effects by activating μ-opioid and κ-opioid receptors, respectively. Capsaicin does not affect the opioid system. (Choice F) Neuropeptide Y (NPY) is a polypeptide neurotransmitter found in the central and autonomic nervous systems. It is thought to play a role in appetite and pain perception. NPY antagonists have been investigated as potential antiobesity drugs. Educational objective: Topical capsaicin causes defunctionalization of afferent pain fibers and depletion of substance P. Initial application results in a burning and stinging sensation, but chronic exposure leads to reduced pain transmission. __________ References: Diagnosing and managing postherpetic neuralgia. (http://www.ncbi.nlm.nih.gov/pubmed/23038608) Topical capsaicin for pain management: therapeutic potential and mechanisms of action of the new high-concentration capsaicin 8% patch. (http://www.ncbi.nlm.nih.gov/pubmed/21852280)

A 65-Year-Old Woman Comes to the Office to Discuss Pain