PAIN IN NEUROMYELITIS OPTICA IS AN UNDER–RECOGNISED BUT DISABLING SYMPTOM

Background Neuromyelitis Optica (NMO) is an autoimmune inflammatory demyelinating disorder of the central nervous system that affects the optic nerve and spinal cord: frequent relapses and the absence of full remission leads to accumulation of deficits and rapid progression of disability. Despite severe weakness and other features of myelitis, patients often describe pain as their most disabling symptom. The aim of the study was to assess any disparity between neurology clinical consultation (and its documentation) and a dedicated interview focussing on the presence and quality of pain in a specialist NMO service. Method A retrospective case note review of all patients attending the national NMO clinic at the Walton Centre, Liverpool UK, April- July 2011 was performed in all patients for documentation of pain by an investigator (SZ). A second independent investigator (KM) performed a structured interview and administered the Brief Pain Inventory (BPI) to assess neuropathic pain. Results 61 patients and their respective records were assessed by both investigators: 45 were diagnosed with NMO and 16 NMO spectrum (only patients who had at least one episode of myelitis were included). AQP4 antibody was present in 72% patients. MRI showed lesions in the cervical or upper-thoracic cord most commonly. The case note review documented neuropathic pain in 23/61 (38%) patients. In these patients documentation of the location of pain was 100%, whilst duration (21%), quality (62%), severity (26%), temporality (31%) and exacerbating/relieving factors (45%) were less frequently recorded. However using the BPI, 37/61 (61%) patients reported neuropathic pain (ie. pain in 38% of patients was not documented to have been recognised): 23/37 (62%) had constant pain. Areas of worst pain were in the legs in 81% (predominantly bilateral), arms (35%), back of trunk (73%), front of trunk (22%) and base of skull/neck (19%). On a scale of 0 to 10, mean severity for worst pain experienced in the last 24 hours was 5.3 (±3.2 SD), with the average pain scored at 3.6 (±2.8 SD). Response to analgesia gave a mean pain reduction of 46% (±35% SD). Pain significantly affected QoL (defined as >5 on a scale of 0 to 10) in terms of: general activity (44%), mood (38%), walking ability (38%), enjoyment of life (32%), normal work (29%), relation with others (29%) and sleep (15%). Conclusion Though neuropathic pain is an important symptom of NMO, the clinician faced with gamut of symptoms associated with typical myelitis (weakness, stiffness, numbness incontinence, immobility, social issues) can overlook pain in many patients (38% of documented cases) in this study. The study also confirms that pain can be severe, is often constant, and significantly affects QoL. The use of a validated questionnaire such as the BPI is recommended and is now part of the routine assessment of all new NMO cases referred to in the Walton centre multidisciplinary NMO clinic.