Whilst some studies have examined aspects of pain in the context of nerve injury (and very rarely in relation to inherited channelopathies), these do not go beyond more than simple measurement of pain intensity or sensory characteristics and there is only a limited literature which has explored the interactions between pain, psychological status and quality of life. Neuropathic pain in general is associated with multiple psychological problems which impact upon quality of life. These include circadian rhythm disturbances (e.g. sleeping difficulty: moderate to severe in 60% of patients), lack of energy (55%), drowsiness (39 %) and difficulty in concentration (36%); similar findings have been specifically documented in erythromelalgia. A poor health perception, poor physical functioning, a high prevalence of role limitation (physical and emotional), as well as, depressive symptoms (based on the pain catastrophising scale and on the Center for Epidemiologic Studies Depression Scale) were all found in patients with Erythromelalgia. In general, beliefs and fears concerning the pain and its implications contribute substantially to determining mood and behaviour. Since neuropathic pain is relatively common in the context of peripheral neuropathy the question arises as to what extent pain is the driver of these co-morbidities - the answer to this is not known, but large randomised controlled trials of analgesic interventions in neuropathic pain states indicate that as pain intensity reduces so does the severity of these co-morbidities. To answer this question the investigators will first need to identify specific tools for the measurement of neuropathic pain co-morbidity in the context of painful channelopathies this is one of the aims of this proposal and they will evaluate a variety of existing assessment tools. Another issue is that it is likely that psychological co-morbidity influences the self reporting of pain intensity, which is a usual primary outcome measure in clinical trials of neuropathic pain analgesic agents.