[Differentiation of pain-related and morphine related impairment of cognitive performance and mood in bone marrow transplantation patients].

AIMS: Severe pain of mucositis induced by cytostatic conditioning therapy in bone marrow transplantation (BMT) patients generally requires continuous parenteral opioid treatment. Cognitive and psychological disturbances are frequent complications subsequent to BMT and may result from cerebral opioid side effects. The aim of the study was to evaluate the efficiency of continuous morphine in mucositis pain and the side-effects in BMT patients. Particular emphasis was placed on the question of whether reaction times, which are usually measured to estimate opioid effects upon vigilance, are influenced by pain-induced cognitive impairments in pain patients.
METHODS: While in hospital, 10 BMT patients were examined daily with the aid of a mucositis scale, subjective visual analog scales (VAS) for pain and mood parameters, a German version of the McGill pain questionnaire (MPQ), and a mental performance task battery, and the morphine given was documented. Mental performance tests were simple auditory reaction time and choice reaction time. Seven patients also performed a Sternberg memory search test in which they had to use 'yes' and 'no' response keys to match visually presented test letters to a previously memorized set of letters. Practice and baseline data were collected within the first week before BMT.
RESULTS: The intensity and duration of mucositis differed from patient to patient, resulting in different pain intensities and MPQ scores. Prolongation of the choice reaction time averaged over the period of mucositis treatment correlated significantly with residual pain intensity (Spearman r(s) = 0.88, p < 0.01) but not with morphine dose (r(s) = 0.35, p = 0.33). For the Sternberg memory search test greater correlation coefficients resulted between reaction time and morphine dose (r(s) = 0.86, p = 0.014) than between reaction time and residual pain intensity (r(s) = 0.61, p = 0.15). In turn, pain intensity, unlike morphine dose, was significantly correlated with high scores in the mood parameters for depression, passivity, and tiredness.
CONCLUSIONS: It is concluded that both pain and morphine can impair cognitive performance, but that these mental stressors seem to differ according to qualitative criteria. Whereas pain might slow reaction time by distracting a patient's attention, particularly in low mental demand tasks, morphine could interfere with more specific cognitive processes, such as short-term memory operations, that are required in more complex tasks.