Nationwide Survey of Atopic Myelitis and Plexin D1-Immunoglobulin G-Related Pain.
To elucidate the features of plexin D1-immunoglobulin (Ig)G-associated neuropathic pain and its relationship to atopic myelitis (AM) in a nationwide Japanese survey. A preliminary survey questionnaire was sent to 1574 selected departments (neurology and pediatrics/pediatric neurology) to explore the numbers of AM and plexin D1-IgG-positive patients between 2018 and 2022. A secondary survey collected detailed patient data via a questionnaire. In the preliminary survey, 987 (62.7%) institutions responded, reporting 87 AM patients (49 women) and 11 plexin D1-IgG-positive non-AM patients (8 women). The secondary survey collected 71 AM (plexin D1-IgG-positive: 6/31) and 11 plexin D1-IgG-positive non-AM patients (83.7% recovery rate). In AM, paresthesia/dysesthesia was most frequently experienced (> 90%), followed by pain (> 70%). The underlying diseases in 17 plexin D1-IgG-positive patients, all of whom had neuropathic pain, were AM and small fiber neuropathy in 6 each, neuromyelitis optica spectrum disorder with aquaporin-4-IgG in 2, and painful trigeminal neuropathy, erythromelalgia, and multiple sclerosis in 1 each. When 14 plexin D1-IgG-positive patients (excluding 3 patients with established demyelinating diseases) were compared with 25 plexin D1-IgG-negative AM patients, onset ≥ 50 years old, pain at onset, and allodynia/erythromelalgia/facial pain during the entire disease course were significantly more common in the plexin D1-IgG-positive group. Conversely, atopic disorders and hyperIgEemia were associated with plexin D1-IgG-negative AM but not plexin D1-IgG-positive patients. Both AM and plexin D1-IgG-positive patients present long-standing neuropathic pain, whereas plexin D1-IgG is particularly associated with aged-onset neuropathic pain, allodynia, erythromelalgia, and facial pain, but not atopy.