REVIEW published: 21 August 2020 doi: 10.3389/fneur.2020.00778 Pain in NMOSD and MOGAD: A Systematic Literature Review of Pathophysiology, Symptoms, and Current Treatment Strategies Susanna Asseyer 1,2, Graham Cooper 1,2,3 and Friedemann Paul 1,2,3,4*† 1 Experimental and Clinical Research Center, Max Delbrück Center for Molecular Medicine and Charité—Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Berlin Institute of Health, Humboldt—Universität zu Berlin, Berlin, Germany, 2 NeuroCure Clinical Research Center, Charité—Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Berlin Institute of Health, Humboldt—Universität zu Berlin, Berlin, Germany, 3 Einstein Center for Neurosciences, Berlin, Germany, 4 Department of Neurology, Charité—Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Berlin Institute of Health, Humboldt—Universität zu Berlin, Berlin, Germany Neuromyelitis optica spectrum disorders (NMOSDs) and myelin oligodendrocyte glycoprotein-antibody-associated disease (MOGAD) are autoimmune inflammatory disorders of the central nervous system (CNS). Pain is highly prevalent and debilitating in NMOSD and MOGAD with a severe impact on quality of life, and there is a critical Edited by: need for further studies to successfully treat and manage pain in these rare disorders. In Dalia L. Rotstein, NMOSD, pain has a prevalence of over 80%, and pain syndromes include neuropathic, University of Toronto, Canada nociceptive, and mixed pain, which can emerge in acute relapse or become chronic Reviewed by: during the disease course. The impact of pain in MOGAD has only recently received Natalie Elizabeth Parks, Dalhousie University, Canada increased attention, with an estimated prevalence of over 70%. These patients typically Courtney Sarah Casserly, experience not only severe headache, retrobulbar pain, and/or pain on eye movement University of Western Ontario, Canada in optic neuritis but also neuropathic and nociceptive pain. Given the high relevance *Correspondence: Friedemann Paul of pain in MOGAD and NMOSD, this article provides a systematic review of the [email protected] current literature pertaining to pain in both disorders, focusing on the etiology of their †ORCID: respective pain syndromes and their pathophysiological background. Acknowledging Friedemann Paul the challenge and complexity of diagnosing pain, we also provide a mechanism-based orcid.org/0000-0002-6378-0070 classification of NMOSD- and MOGAD-related pain syndromes and summarize current Specialty section: treatment strategies. This article was submitted to Keywords: aquaporin 4, headache, myelin oligodendrocyte glycoprotein-antibody-associated disease, Neuroepidemiology, neuromyelitis optica spectrum disorders, neuropathic pain, pain, painful tonic spasms a section of the journal Frontiers in Neurology Received: 13 January 2020 INTRODUCTION Accepted: 24 June 2020 Published: 21 August 2020 In 1894, Eugène Devic (1858–1930) and his doctoral student Fernand Gault (1873–1936) reported Citation: a historical case on a patient with optic neuritis (ON) and myelitis and proposed the name “neuro- Asseyer S, Cooper G and Paul F myélite optique” for this syndrome. The patient, a 45-year-old woman, was admitted for suspected (2020) Pain in NMOSD and MOGAD: “neurasthenia,”suffering from disturbed sleep, gastrointestinal symptoms, neuromuscular asthenia, A Systematic Literature Review of Pathophysiology, Symptoms, and palpitations, and, especially, headache: “The pain occurs in attacks, both during the day and night. Current Treatment Strategies. Pain attacks may be long or short, affecting one side of the face and the head, sometimes the right side, Front. Neurol. 11:778. mostly the left, but the highest intensity is always at the occipital region: the neck and eyeballs. The doi: 10.3389/fneur.2020.00778 pain is sometimes so strong that it causes the patient to cry.” Frontiers in Neurology | www.frontiersin.org 1 August 2020 | Volume 11 | Article 778 Asseyer et al. Pain in NMOSD and MOGAD One month after admission, the patient suddenly developed disease with seizures (33, 38–44). Pain is also becoming acute complete paraparesis and visual loss. It is currently a matter increasingly recognized as a common and debilitating symptom of debate whether the patient suffered from a neuromyelitis in MOGAD. However, data in pain in MOGAD are scarce and optica spectrum disorder (NMOSD) or a myelin oligodendrocyte have to be verified in larger studies: mild chronic pain has a glycoprotein-antibody-associated disease (MOGAD) (1). reported prevalence of 86% (2), and severe acute pain in the Terrible, agonizing, and unbearable pain can arise as an acute or context of attacks has a prevalence of 70% (38). Furthermore, chronic symptom in both pathologies (2–4)(Table 1). in addition to the typical retrobulbar pain and/or pain on eye Neuromyelitis optica spectrum disorders (NMOSDs) are rare movement, severe and sometimes migraine-like headache can and, in most cases, relapsing inflammatory diseases of the precede visual loss in MOG-Ab-related ON (45, 46), the most- central nervous system (CNS) (10). In the majority of cases, common clinical feature at onset and subsequent relapse (33, 37, NMOSDs are associated with serum immunoglobulin G (IgG) 38, 47, 48). autoantibodies (Abs) targeting the astrocyte aquaporin-4 (AQP4) Pain is a very common feature of both diseases and has a water channel (11, 12). Patients typically suffer from recurrent higher prevalence and severity compared to multiple sclerosis attacks of severe optic neuritis and/or myelitis (13, 14) and, less (MS), where estimates of pain prevalence are ∼50% (18, 27, 49). frequently, brainstem or brain involvement (15, 16), leading to It also has a severe impact on the quality of life of affected a diverse range of symptoms, of which severe pain is one of patients (2, 18, 26, 27), interfering with physical, emotional, and the most frequent and disabling (2, 17–26). Chronic pain occurs cognitive aspects of well-being (2, 27, 50), as well as activities of in NMOSD with an estimated prevalence between 72 and 86% daily life in NMOSD (60–83% AQP4-Ab positive) and MOGAD (2, 18, 27, 28). Over 50% of NMOSD (82% APQ4-Ab positive) (2, 18, 26, 27). The higher the pain intensity, the worse the patients recalled an increase in pain intensity as the first indicator physical and emotional quality of life (2, 51). of a relapse (26) and 25% of patients with NMOSD (82% AQP4- The alleviation of pain through careful management and Ab positive) reported pain as their worst symptom, despite also treatment should lead to significant improvement in the quality experiencing severe weakness and bladder or bowel dysfunction of life of patients with NMOSD and MOGAD. However, (26). Neuropathic pain is the most common type of chronic pain successfully controlling pain is highly challenging in these with a prevalence of up to over 80% (2, 26), and painful tonic disorders (2, 26–28), and there is relatively little published spasms occur with a prevalence of 25–40% (29–32). literature on therapeutic intervention or treatment of pain MOGAD is another inflammatory autoimmune condition of as a primary outcome in these patient groups. In order to the CNS, defined by IgG antibodies against conformationally highlight this and facilitate future research in this critical area, intact myelin oligodendrocyte glycoprotein (MOG) localized on we conduct a systematic review of the current literature on the surface of the myelin sheaths (13, 33, 34). Although there different pain syndromes in NMOSD and MOGAD. Based on is some phenotypic overlap with AQP4-Ab-positive NMOSD, this, we propose a mechanism-based classification of NMOSD- most researchers consider MOGAD to be a distinct disease and MOGAD-related pain and additionally evaluate current entity (35–37). Affected patients may develop any combination of treatment strategies. acute disseminated encephalomyelitis, transverse myelitis (long or short), optic neuritis (ON, typically anterior, often bilateral), brainstem pathology often affecting cerebellar peduncles, cranial METHODS nerve involvement, and, less frequently, brainstem encephalitis, encephalitis mimicking small vessel CNS vasculitis, and cortical We performed a search of PubMed (last updated on June 09, 2020), combining neuromyelitis optica or neuromyelitis optica spectrum disorders AND pain, as well as myelin oligodendrocyte glycoprotein AND pain. Additional searches were performed TABLE 1 | Characteristics of different pain types. combining neuromyelitis optica and myelin oligodendrocyte glycoprotein, respectively, AND headache or dysesthesia or Pain Pain is defined as an “unpleasant sensory experience associated with actual or potential tissue damage or dystonia or Lhermitte’s sign or neuralgia or spasms or spasticity. described in terms of such damage” (5). This search was limited to English language publications and Nociceptive Nociceptive pain occurs as an appropriate encoding of yielded a total of ∼200 articles including case reports, original pain noxious or potentially noxious stimuli. It represents a clinical studies, and reviews, which were reviewed by title and physiological response that the patient becomes abstract for potential relevance to this topic. When the title conscious of when nociceptors in bone, muscle, or any and abstract did not clearly indicate the degree of relevance body tissue are activated, warning the organism of tissue damage. In response, coordinated reflexes and to the