Table 1.
Steps in the process to validate the MS diagnoses recorded in the Swedish National Patient Register (NPR) (2001–2013) (n = 19,781)a by two sequential register-based case-definition algorithms
| N identified (i.e., confirmed MS) | N remaining (i.e., uncertain MS) | |
|---|---|---|
| Primary case-definition algorithm | ||
| (1) Identify those with an MS diagnosis in the SMSReg (up through 31 December 2014) | 14,033 | 5748 |
| (2) Identify those with ≥ 3 visits ever with MS diagnoses in the NPR (1987–2013) | 3659 | 2089 |
| (3) Identify those with a specific MS medication ATC code (Tysabri (Natalizumab): L04AA23, Pegylerat interferon beta1-a (Plegredy): L03AB13, Teriflunomid (Aubagio): L04AA31, and Fingolimod (Gilenya): L04AA27) in the SPDR (1 July 2005–31 December 2013) | 6 | 2083 |
| (4) Identify those on disability pension due to MS as main or secondary diagnosis according to MiDAS (up through May 2015) | 158 | 1925 |
| (5) Identify those who had a new sickness absence spell due to MS according to MiDAS after 30 days from the first MS diagnosis date (January 2005–May 2015) | 51 | 1874 |
| (6) Identify those with an MS diagnosis as the main or contributing cause of death in the CDR (up through December 2016) | 15 | 1859 |
| Subtotals from the primary case-definition algorithm | 17,922 | 1859 |
| Secondary case-definition algorithm | ||
| (1) Identify those who have had previous visits with MS-like symptoms according to the NPR (ICD-10: Z03.3, R20.2, R42, R53, H47.5, and H48) if the first MS diagnosis was recorded in the last 2 years of the study periodb | 177 | 1682 |
| (2) Identify those who committed suicide (including suspected) or died according to the CDR within 1 year after the first MS diagnosis | 33 | 1649 |
| (3) Identify those who emigrated within 2 years after the first or second MS diagnosis, according to LISA | 28 | 1621 |
| (4) Identify those who immigrated the year before or the same year as the first MS diagnosis, according to LISA | 15 | 1606 |
| (5) Identify those who had an MS diagnosis in the last 3 years (2011–2013) of the NPR if there were less than 2 years between the 2 visits with MS diagnoses | 116 | 1490 |
| Subtotals from the secondary case-definition algorithm | 369 | 1490 |
| Total | 18,291 | 1490 |
ATC Anatomical Therapeutic Classification, CDR Cause of Death Register, ICD International Classification of Diseases, LISA Longitudinal Integration Database for Health Insurance and Labour Market Studies, MiDAS Micro-Data for Analysis of the Social Insurance System Register, MS multiple sclerosis, NPR National Patient Register, SPDR Swedish Prescribed Drug Register, SMSReg Swedish MS Register
aAll individuals with a record of an MS diagnosis registered during 1 January 2001 and 31 December 2013 as per ICD-10 (G35) in the Swedish National Patient Register and aged 16–64 at first diagnosis in the study period
bZ03.3: Observation for suspected nervous system disorder, R20.2: Paraesthesia of skin, R42: Dizziness and giddiness, R53: Malaise and fatigue, H47.5: Disorders of other visual pathways, and H48: Disorders of optic nerve and visual pathways in diseases classified elsewhere