Table 2.

Characteristics of individuals identified during 1 January 2001–31 December 2013 with an MS diagnosis registered in the Swedish National Patient Register (NPR)^a when aged 16–64, according to the register-based case-definition algorithms

	Provisional MS diagnoses in the NPR		Uncertain MS as per Primary case-definition algorithm		Uncertain MS as per Secondary case-definition algorithm		Confirmed MS as per both case-definition algorithms		χ2 test
	n = 19,781		n = 1859b		n = 1490b		n = 18,291		p valuec
	n	%	n	%	n	%	n	%
Sex									< 0.001
Women	13,743	69.5	1224	65.8	970	65.1	12,773	69.8
Men	6038	30.5	635	34.2	520	34.9	5518	30.2
Healthcare setting of first recorded visit in the NPR with MS									0.166
In-patient Register	3623	18.3	322	17.3	253	17.0	3370	18.4
Out-patient Register	16,158	81.7	1537	82.7	1237	83.0	14,921	81.6
Main diagnosis as MS for the first recorded visit	17,738	89.7	1520	81.8	1211	81.3	16,527	90.4	< 0.001
Number of visits in the NPR with MS everd									< 0.001
< 3	2834	14.3	1859	100.0	1490	100.0	1344	7.3
≥ 3	16,947	85.7	c	c	c	c	16,947	92.7
In the NPR prior to 1 January 2001 with MS	4399	22.2	29	1.6	28	1.9	4371	23.9	< 0.001
Died (all-cause) during 2001–2013	1806	9.1	96	5.2	65	4.4	1741	9.5	< 0.001
Age at first record with MS in the NPR during 2001–2013
16–20	508	2.6	42	2.26	31	2.08	477	2.61
21–25	1072	5.4	91	4.90	73	4.90	999	5.46
26–30	1813	9.2	168	9.04	127	8.52	1686	9.22
31–35	2138	10.8	202	10.87	155	10.40	1983	10.84
36–40	2397	12.1	201	10.81	174	11.68	2223	12.15
41–45	2686	13.6	219	11.78	173	11.61	2513	13.74
46–50	2621	13.3	234	12.59	181	12.15	2440	13.34
51–55	2731	13.8	243	13.07	201	13.49	2530	13.83
56–60	2451	12.4	273	14.69	224	15.03	2227	12.18
61–64	1364	6.9	186	10.01	151	10.13	1213	6.63

ICD International Classification of Diseases, MS multiple sclerosis, NPR National Patient Register

^aIdentified by ICD-10 code G35 registered as the main or side diagnosis for in-patient and specialised out-patient care in the NPR. Inclusion criteria: All individuals with a record of a prevalent MS diagnosis registered in the Swedish NPR and aged 16–64 years at the time of the first code appearing during the study period 1 January 2001 and 31 December 2013, n = 19,781

^bn = 369 individuals were plausible MS as per the second case-definition algorithm and thus many individuals in the primary and secondary algorithm groups overlap

^cSignificantly different proportions between the confirmed MS (both algorithms) and uncertain MS as per secondary algorithm, as tested by Chi square tests with alpha set at 0.05

^dStep 3 of the primary-case definition algorithm was to identify individuals with > 3 visits ever recorded in the NPR with MS as confirmed MS