Unexplained lower limb pain in Parkinson's disease: A phenotypic variant of "painful Parkinson's disease"

Unexplained pain is a key non-motor symptom (NMS) of Parkinson's disease (PD) that is prevalent throughout the condition and often unrecognized and under treated. We have identified a cluster of patients with unexplained refractory and intrusive lower limb pain. Methods: Patients with 'unexplained' pain were identified from a survey using a non-motor symptom questionnaire and scale (NMSQuest, NMSS). Patients reporting unexplained severe proximal lower limb pain were then assessed using a newly devised PD pain scale. Co-morbid conditions were excluded and all had lower spine imaging. Results: From a cohort of 225 patients we have identified 22 with unexplained lower limb pain described as persistent leg pain ranging from unilateral to bilateral sometimes associated with whole body pain. None had significant spinal pathology or evidence of large fiber neuropathy. 14 were on regular analgesics with poor effect while 9 took morphine based remedies. Severe unremitting pain led to accidental overdose and death in one patient. All took a combination of levodopa and dopamine agonist treatment including 3 on intrajejunal levodopa infusion. All had high NMSQuest (mean = 17/30) and NMSS (mean = 95 (normal range 30-60)) scores. Conclusions: We believe that unexplained lower limb pain is a specific non-motor phenotype in Parkinson's disease that is problematic and often undisclosed. This may be a variant of central pain and merits recognition. (C) 2013 Elsevier Ltd. All rights reserved.