The cold pressor test (CPT) has been used in experimental paradigms to measure pain tolerance. It is used clinically to evaluate for opioid-induced hyperalgesia (OIH), as part of the clinical evaluation of fibromyalgia, to document reversal of OIH by low dose naltrexone (LDN), and to document the clinical response of fibromyalgia to LDN.
We reviewed charts of 254 outpatients admitted to addiction medicine with chronic opioid treatment for pain, opioid addiction, or fibromyalgia. Controls were 46 non-addicted support persons. We invented the term "morphine years," a year at 60 mg/day, to estimate opioid exposure.
The mean age of patients was 41.4 years and controls 51.5. Age was not significantly correlated with CPT within each group. Female patients' mean CPT score (in seconds) was 35.0, male patients' 56.1, female controls' 110.8, male controls' 114.3. More morphine years correlated with younger age, more depression, higher prevalence of borderline personality disorder and attention deficit hyperactivity disorder, and low CPT. LDN increased CPT and reduced pain symptoms for both opioid users and fibromyalgia patients, with the increase being significantly higher for opioid users.
CPT is shown to be an objective test of pain tolerance with clinical applications: evaluation of OIH, evaluation of fibromyalgia, reversal of OIH, protracted withdrawal with LDN, and amelioration of fibromyalgia with LDN.
CPT is an objective complement to the subjective FACES pain scale. It gives an objective measure of changes in pain sensitivity accompanying administration of LDN. Limitations of a case series report are noted.