Scrambler Trial for Pain in NMOSD

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease of the central nervous system that disproportionately affects non-Caucasians and females,1,2 and has a worldwide prevalence estimated to be 0.52 to 4.4/100,000.3 NMOSD preferentially causes recurrent inflammatory attacks in the optic nerves and spinal cord, leading to blindness, paralysis and death. Despite these devastating consequences of the disease, patients have reported that pain is among the most prevalent and debilitating symptom, and impacts mood, mobility and quality of life (QoL). In particular, central neuropathic pain (CNP) is pervasive, severe, intractable to treatment, and affects 62-91% of patients with NMOSD. CNP is described as agonizing burning, stabbing, shooting, tingling or squeezing sensation that is distressing, persistent and incapacitating.13,14 The presence of CNP in NMOSD is a direct consequence of targeted immune-mediated destruction of the spinal cord and may be influenced by lesion span and location: NMOSD lesions are generally transverse, involving both the central gray matter and dorsal horns. The dorsal horns are innervated by primary ascending fibers that convey sensory information to the brain. Damage to the central gray matter in NMOSD leads to astrocytic damage and tissue necrosis, thus disrupting sensory pain tracts going to and from the brain. As a consequence of ongoing spontaneous activity arising in the periphery, surviving neurons develop increased background activity and increased responses to ascending nerve impulses, including normally harmless tactile stimulation. An additional mechanism of CNP involves peripheral sensitization of non-myelinated ascending C fibers interpreted by the brain as persistent pain, a characteristic sign of an inflammatory process in the spinal cord.

Spinal CNP typically presents weeks to months after the cord damage has occurred, long after the acute injury, and may be the result of secondary changes due to reorganization of damaged circuits of the somatosensory system. CNP occurs at and below the spinal cord lesion level, and can persist for years, decades or throughout the patient's life. As with neuropathic pain from other etiologies, the most frequently-used medications for its treatment in NMOSD are anti-epileptics, antidepressants and non-steroidal anti-inflammatory agents. Descriptive studies in NMOSD recognized the inadequate effect of these medications, resulting in frequent breakthrough opioid use. Furthermore, side effects from these medications, particularly at higher doses, are independently associated with fatigue.

Scrambler is a type of transcutaneous electrostimulation (TENS) that uses peripheral nerve stimulation to modify ascending sensory responses in the spinal cord. Electrical impulses are transmitted via surface electrodes placed surrounding the pain area. Traditional TENS units take advantage of the Gate Control Theory in which stimulation of surrounding A-delta fibers dampens incoming pain signals. Scrambler therapy provides additional stimulation of ascending sensory C fibers that imitate normal nerve action potentials with the intent of re-organizing maladaptive signaling pathways. The theory behind Scrambler treatment is that "scrambled" waveforms - instead of repetitive identical waveforms in traditional TENS - are dynamically assembled into strings of information that are interpreted by the brain to replace pain with "no-pain" information. In contrast to traditional TENS therapy that provides only short term pain relief, studies with Scrambler therapy in peripheral neuropathy suggest that patients can have significantly reduced pain or be pain-free for up to 3 months following a series of treatments, and that follow-up treatments may require fewer sessions for continued relief.

This study is a randomized single blinded, sham-controlled trial of patients with Neuromyelitis Optica Spectrum Disorder who have central neuropathic pain using Scrambler Therapy added to standardized empiric medications using patient reported outcomes to determine if Scrambler Therapy is a feasible and effective add-on treatment of chronic neuropathic pain.

This trial will recruit twenty-two adult patients diagnosed with NMOSD who have chronic neuropathic pain despite empiric treatment with an anti-epileptic, antidepressant, opioid and/or an NSAID medication. Patients will be randomized 1:1 to undergo Scrambler Therapy or blinded sham daily for 10 days. The primary outcomes will be acceptability and feasibility. The secondary outcome will be efficacy measured as a change in pain scores of more than two points recorded daily by the patient using an 11-point visual analog scale; quality of life (QoL), neurologic function, anxiety, depression, sleep disturbance and pain will also be evaluated at baseline, at the end of therapy, and at 4 \& 8 weeks following completion of treatment. Investigators hypothesize that Scrambler Therapy will be an acceptable, feasible and efficacious intervention that significantly reduces pain in patients with neuromyelitis optica spectrum disorder.