How are allodynia and hyperalgesia clinically distinguished?

• A. Allodynia: pain from non-painful stimuli; Hyperalgesia: increased pain from painful stimuli
• B. Hyperalgesia: pain from non-painful stimuli; Allodynia: increased pain from painful stimuli
• C. Allodynia and hyperalgesia are the same condition
• D. Allodynia is decreased pain to nonpainful stimuli

Answer: (A)

Distinguishing allodynia from hyperalgesia hinges on what kind of stimulus evokes pain and how intense that pain is.

Allodynia means a normally non-painful stimulus causes pain—for example, light touch, a gentle breeze, or a shirt rubbing the skin producing a painful sensation in neuropathic or sensitized states. Hyperalgesia means an ordinarily painful stimulus produces more pain than expected—for instance, a pinprick causing exaggerated pain, even though the stimulus is within the usual painful range. These reflect different patterns of sensitization and processing in the nervous system: allodynia often points to abnormal central processing of non-noxious input, while hyperalgesia can reflect heightened responsiveness to nociceptive input at the site of injury (and sometimes broader central amplification).

The other descriptions would swap the definitions or describe a decreased pain response, which doesn’t fit how these terms are used clinically.