Signs of hyperpathia in chronic peripheral neuropathic pain

BackgroundNeuropathic pain is pain due to a disease or lesion of the somatosensory system, and can be either spontaneous, evoked or both. Hyperpathia is a type of evoked pain defined by IASP as ‘a painful syndrome characterized by an abnormally painful reaction to a stimulus, especially a repetitive stimulus, as well as an increased threshold’. The literature is sparse, and definitions are unclear and inconsistent.MethodsThe aim of this study was to examine for the presence of mechanical hyperpathia in a heterogeneous group of patients with peripheral neuropathic pain and correlate signs of hyperpathia with other sensory signs. Patients were examined with graded pinprick stimuli to obtain a stimulus–response curve and repetitive pinprick stimuli to assess increase in pain over time and aftersensations. Then, patients were grouped based on the likelihood of having mechanical hyperpathia with either a steep stimulus–response curve or a steep curve on the repetitive pinprick test and results were correlated to mechanical detection and pain thresholds and other outcomes from a full quantitative sensory testing.ResultsWe included 124 patients with documented peripheral neuropathic pain. Patients with a steep stimulus–response curve did not overlap with patients with a steep curve on the repetitive pinprick test and both groups more often had decreased rather than increased detection and pain thresholds.ConclusionsOur study questions the concept of hyperpathia and suggests that more studies are needed to identify which symptoms and signs group together and might form a syndrome.Significance StatementHyperpathia is a syndrome of evoked pain. It is poorly defined and little is known about its clinical presentation. Since it is part of pain symptomatology it is important to have a clear definition and understand the pathophysiology behind. This study explored signs of hyperpathia in a heterogeneous group of patients with peripheral neuropathic pain. We used stimulus–response function and repetitive pinprick stimulation to group patients based on the IASP definition. More studies are needed to understand how symptoms and signs coincide.