AQP4 and nervous system disorder: The ALS and NMOSD were rare neurological diseases; recent studies reported that the prevalence of ALS and NMOSD were 3.43/100,000 and 2.56/100,000, respectively.[6,7] Therefore, the coexistence of ALS and NMOSD was exceedingly rare, there have been only 2 case reports; 1 case with NMOSD preceding the onset of ALS, the other case with long-standing ALS who later developed transverse myelitis (Table 1).[8,9] In this case, she was diagnosed as having ALS before the onset of NMOSD, but there was an asymptomatic AQP4 positive period for 6 years.