Table 2. Univariable exponential AFT model with shared gamma frailty for the identification of predictors of time to next attack (inter-attack interval).

	Independent variables			Unadjusted time ratio (95% CI)	p-value
	Demographics
		Sex (Ref: female)		1.21 (0.67-2.20)	0.530
		Disease duration		1.34 (1.16-1.56)	0.038
		Age at disease onset		1.01 (1.00-1.01)	0.813
		Age at the most recent attack		1.00 (0.98-1.01)	0.666
		Cumulative number of attacks		1.34 (1.16 - 1.56)	0.000
	First attack, location
		Optic nerve		0.82 (0.53-1.26)	0.368
		Spinal cord		1.15 (0.75-1.76)	0.533
		Brain		0.97 (0.5-1.91)	0.938
	Most recent attack, location
		Optic nerve		0.56 (0.37-0.84)	0.005
		Spinal cord		1.63 (1.09-2.44)	0.018
		Brain		1.00 (0.53-1.89)	0.997
	Treatment (Ref: no treatment)
		Pd, duration of Tx	<6 Mo	1.04 (0.65-1.66)	0.883
			≥6 Mo a	1.64 (0.91-2.98)	0.102
			Continued Tx	2.97 (1.48-5.99)	0.002
		AZA, dosage b		1.68 (1.19-2.37)	0.003
		AZA and Pd, combined Tx	AZA with <6 Mo Pd	0.65 (0.26-1.64)	0.366
			AZA with ≥6 Mo Pd a	7.45 (1.00-55.72)	0.050
			AZA with continued Pd	6.00 (1.85-19.5)	0.003
		Rituximab		6.06 (1.74-21.17)	0.005
		Interferon beta		0.64 (0.39-1.08)	0.093
		Cyclophosphamide		2.88 (0.81-10.21)	0.102
		Mycophenolate		1.56 (0.36-6.68)	0.549
		Mitoxantrone		1.71 (0.45-6.54)	0.432
		Methotrexate		1.93 (0.40-9.39)	0.415

Abbreviations: AFT, accelerated failure time; AQP4-Ab, aquaporin-4 autoantibody; AZA, azathioprine; CI, confidence interval; F, female; M, male; Mo, month; NMO, neuromyelitis optica; other NMOSD, neuromyelitis optica spectrum disorder other than NMO; Pd, oral prednisolone; Ref, reference value; Tx, treatment

^a Oral prednisolone was discontinued before the next attack

^b Analyzed as a linear variable