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The assessment of somatosensory function is a cornerstone of research and clinical practice in neurology. Recent initiatives have developed novel protocols for quantitative sensory testing (QST). Application of these methods led to intriguing findings, such as the presence lower pain-thresholds in healthy children compared to healthy adolescents. In this article, we (re-) introduce the basic concepts of signal detection theory (SDT) as a method to investigate such differences in somatosensory function in detail. SDT describes participants’ responses according to two parameters, sensitivity and response-bias. Sensitivity refers to individuals’ ability to discriminate between painful and non-painful stimulations. Response-bias refers to individuals’ criterion for giving a “painful” response. We describe how multilevel models can be used to estimate these parameters and to overcome central critiques of these methods. To provide an example we apply these methods to data from the mechanical pain sensitivity test of the QST protocol. The results show that adolescents are more sensitive to mechanical pain and contradict the idea that younger children simply use more lenient criteria to report pain. Overall, we hope that the wider use of multilevel modeling to describe somatosensory functioning may advance neurology research and practice.
Introduction:
Many patients with cerebral palsy (CP) suffer chronic pain as one of the most limiting factors in their quality of life. In CP patients, pain mechanisms are not well understood, and pain therapy remains a challenge. Quantitative sensory testing (QST) might provide unique information about the functional status of the somatosensory system and therefore better guide pain treatment.
Objectives:
To understand better the underlying pain mechanisms in pediatric CP patients, we aimed to assess clinical and pain parameters, as well as QST profiles, which were matched to the patients' cerebral imaging pathology.
Patients and methods:
Thirty CP patients aged 6–20 years old (mean age 12 years) without intellectual impairment underwent standardized assessments of QST. Cerebral imaging was reassessed. QST results were compared to age- and sex-matched controls (multiple linear regression; Fisher's exact test; linear correlation analysis).
Results:
CP patients were less sensitive to all mechanical and thermal stimuli than healthy controls but more sensitive to all mechanical pain stimuli (each p < 0.001). Fifty percent of CP patients showed a combination of mechanical hypoesthesia, thermal hypoesthesia and mechanical hyperalgesia; 67% of CP patients had periventricular leukomalacia (PVL), which was correlated with mechanic (r = 0.661; p < 0.001) and thermal (r = 0.624; p = 0.001) hypoesthesia.
Conclusion:
The combination of mechanical hypoesthesia, thermal hypoesthesia and mechanical hyperalgesia in our CP patients implicates lemniscal and extralemniscal neuron dysfunction in the thalamus region, likely due to PVL. We suspect that extralemniscal tracts are involved in the original of pain in our CP patients, as in adults.