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NBME 24 Answers

nbme24/Block 1/Question#11

A 55-year-old man with type 1 diabetes mellitus ...

Persistent activation of voltage-gated Na+ channels in the nociceptor

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 +8  upvote downvote
submitted by njspix(8),

Per UpToDate, the key here is the allodynia. This patient has intact sensation, it's just "turned up" way too much. The simplest way to explain this is that the sensor itself (the nociceptor) is over-activated.

Note that nociceptive pain (as this is termed) is more often due to inflammation/pressure/tissue damage, whereas neuropathic pain (more central) has a wide variety of causes (diabetes is a prominent one).

 +8  upvote downvote
submitted by seagull(467),

Another approach. Diabetes causes non-enzymatic glycosylation which may negatively impact the function of neurons mainly due to altered blood supply among other things. These glycosylate deposits typically occur peripherally at the legs. The only peripheral answer choice was a nociceptor in the legs. all the other answer choices are at least more centrally located with larger blood supplies.

Again, not perfect but a way to reason out this answer but it does work.

sam1  I believe this concept is referring to peripheral sensitization. Peripheral nerves that have sustained damage (such as through non-enzymatic glycosylation in DM) cause sensitization of their neighboring nerves, thus leading to lower thresholds for activation. This sensitization is thought to be accomplished through mediators such as PGE2. +2  
sam1  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3701208/ ^ Section on peripheral sensitization +1  

Allodynia is central pain sensitization. Triggering of pain by a non painful stimuli. Also seen in Fibromyalgia. [vs Hyperalgesia : Inc response to painful stimuli]

Its a positive (i.e Actively feeling, not lack of feeling) symptpms. so B & C is not the answer. D isnt answer either. as vanilloid receptor (TRPV1) is also afferent nociceptive transmission (modulated by capsaicin). Activation is soon followed by desensitization.

A - IDK. if problem was in DRG there would be lot more symptoms.

madojo  if you are an idiot like me than that long word in option b is GABA +