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NBME 20 Answers

nbme20/Block 4/Question#41

A 56-year-old man with a 20-year history of chronic ...


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Relief of intractable pain was produced in six human patients by stimulation of electrodes permanently implanted in the periventricular and periaqueductal gray matter. The level of stimulation sufficient to induce pain relief seems not to alter the acute pain threshold. Indiscriminate repetitive stimulation produced tolerance to both stimulation-produced pain relief and the analgesic action of narcotic medication; this process could be reversed by abstinence from stimulation. Stimulation-produced relief of pain was reversed by naloxone in five out of six patients. These results suggest that satisfactory alleviation of persistent pain in humans may be obtained by electronic stimulation.

usmleuser007  These questions seem unfair to test because they are based on experimental data. Guess they are there to limit a perfect score. +1  
xxabi  I just read it as patients take opioids to blunt or control pain. So if the electrode does the same thing (decrease pain), then an antagonist of opioids (naloxone) would bring the pain back? Idk if that reasoning is sound but that's the logic I used, I didn't even think of it as experimental. +12  
xxabi  Also its the only one that's an opioid antagonist from the list! +1  
redvelvet  they are writing these questions in an evidence-based manner because the questions in medicine cannot be produced by a self imagination or logic. But that doesn't mean that we have to know their exact evidence like this question. we can use our own basic knowledge and adjust it with logic. so opioids have an analgesic effect in the body and naloxone can revert it. +4  
champagnesupernova3  Anything that reduces pain by brain stimulation is increasing endogenous opiods like endorphins and encephalitis. +1  
champagnesupernova3  Enkephalins* not encephalitis +  

The crux of the question is asking, if the patient feels decreased pain (which is driven by opioid molecules; that's why opioids are administered as painkillers), then how do you stop the inhibition? An opioid antagonist (naloxone is the only one that is an antagonist)

neovanilla  wrong answers: b-endorphin - an endorphin and ACTH hormone (similar to ACTH, POMC) that can bind to the ยต-opioid receptor Enkephalin - a neurotransmitter involved in the indirect basal ganglia pathway (along with GABA); it can also bind to delta-opioid receptors Morphine - an opioid agonist (used for pain relief) Oxycodone - Another opioid agonist (~same potency as morphine) +2  

Maybe the pt was under opiods tx before the surgery and with the administration of naloxone the grade of pain that was relief by opiod but not by the implant comes up. That worked for me