Myelitis in NMOSD may also mimic spinal cancer or lymphoma and vice versa; whenever possible, AQP4-IgG (and MOG-IgG) should be tested and NMOSD excluded before a decision is made to perform spinal cord biopsy—a procedure that can leave patients severely disabled—for suspected spinal neoplasia [180]. The gene discussed is AQP4; the disease is myelitis.