Decrease perception to certain types of painful stimuli in patients with RSD (also called complex regional pain syndrome type 1) is relatively common and has led to confusion and misunderstanding among physicians. In turn, patients can suffer for not receiving appropriate care from health providers or, even worse, the health provider accuses the patient of suffering more from a mental disorder than a genuine neurological disorder. This problem has led to delayed treatment that can lead to a poorer outcome. The phenomenon of altered perception to painful stimuli is illustrated by two patients who have benefited by the administration of ketamine:
Prior to a 3-day treatment with escalating doses of ketamine Janice Beasley had complete numbness in her left lower extremity for 10 years (which makes her more prone to injury). After 3 days of treatment with ketamine on an outpatient basis she had return of sensation for pain (as evidenced in your post treatment pain thresholds). In addition, she began to move her toes for the first time, noted decrease pain and reported healing of open bleeding skin ulcers . She was delighted about re-discovering pain in her left foot.
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Lindsay Spengler demonstrated a different type of altered perception to pain. Light touch was experience as a knife stabbing the skin while poking her skin hard with a blunt instrument caused no pain. She had to sleep in a cardboard box so nothing would touch her skin. After the ketamine coma, light touch caused no pain (no allodynia) and poking her hard with a blunt instrument caused pain as you would expect in a normal person. (Compare Lindsay’s pain thresholds before and after ketamine).
Learn more .... 28-minute video
These cases illustrate why it is important to measure pain thresholds in patients with sensory deficits (unable to experience pain properly) due to RSD before and after treatment with ketamine to see if the patient can return to experience pain as it is in normal people.