Question

Patient had SUN BURN, now takes bath in 40 degree water, and feels pain.

• A. Thermal receptor: hyperalgesia
• B. Innocuous thermal receptor allodynia
• C. Thermal receptor allodynia
• D. Innocuous thermal receptor hyperalgesia

Hint:

Pain from a NON-painful stimulus = allodynia; exaggerated pain from an already-painful stimulus = hyperalgesia. Is 40°C normally painful?

Answer 1

The Correct Option is B

Step 1: Define the two key pain terms.
Allodynia is the perception of pain in response to a stimulus that is normally NOT painful (an innocuous/non-noxious stimulus). Hyperalgesia is an exaggerated (increased) pain response to a stimulus that is normally already painful (a noxious stimulus).

Step 2: Identify the stimulus in this case.
A 40 \(^{\circ}\)C bath is warm but it is NOT a tissue-damaging (noxious) temperature; pain normally begins around 45 \(^{\circ}\)C. Therefore 40 \(^{\circ}\)C is an innocuous (non-noxious) thermal stimulus. After sunburn, the inflamed skin is sensitised, so this normally non-painful warmth is now felt as pain.

Step 3: Apply the definition.
Pain from a normally non-painful (innocuous) warm stimulus = allodynia, and the stimulus is thermal and innocuous. This matches "Innocuous thermal receptor allodynia."

Step 4: Eliminate the distractors.
(A) and (D) use "hyperalgesia," which requires an already-noxious stimulus - 40 \(^{\circ}\)C is not noxious, so hyperalgesia does not fit. (C) correctly says allodynia but omits that the stimulus is innocuous, making (B) the more complete and precise answer; sunburn classically produces sensitisation to innocuous warmth.

Final answer: B - Innocuous thermal receptor allodynia.