Alemtuzumab (ALZ) belongs to the immune reconstitution therapies for relapsing-remitting multiple sclerosis (RRMS). ALZ therapy is associated with an increased risk for secondary autoimmune diseases (SAD), in particular autoimmune thyroid disorders (AITD).
To investigate if the occurrence of thyroid auto-antibodies (Ab), after initiating ALZ treatment, could predict the development of AITD.
All RRMS patients in Sweden initiating ALZ (n=124, 74 females) 2014-2019, were consecutively included in this prospective observational study. Plasma samples were obtained prior to ALZ and at 6, 12 and 24 months of follow-up for analyses of thyroglobulin Ab (TgAb), thyroperoxidase Ab (TPOAb) and thyrotropin receptor Ab (TRAb). Monthly serum samples for free thyroxin and thyroid stimulating hormone, as well as clinical symptoms were followed to detect AITD.
At mean follow-up of 4.5 (SD 1.6) years 50 patients (40%) had developed AITD (43 Graves’ disease). Mean time from baseline to AITD was 2.1 (SD 1.6) years, in 62 % the development of thyroid Ab preceded AITD. At baseline 5% (n=6/114) patients had positive TRAb, 3% (n=3/115) positive TgAb, and 3% (n=3/115) positive TPOAb. Corresponding values at 6 months were 3% (n=2/78), 6% (n=5/85), 5% (n=4/86), at 12 months 14% (n=14/102), 15% (n=15/102), 18% (n=18/102), and at 24 months 22% (n=16/73), 19% (n=15/78), 23% (n=18/78). No treatment was given for AITD in 4% (n=2/50), 14% (n=7/50) had levothyroxine (L-T4) only, 36% (n=18/50) high dose anti-thyroid drug (ATD) with L-T4, 34% (n=17/50) thyroidectomy, 4% (n=2/50) ATD alone, 2% (n=1/50) radioactive iodine and for 6% (n=3/50) data were missing. Mean time from detection of auto-Ab to diagnosis of AITD was 4 (SD 11.3) months. At baseline 9 patients had thyroid Ab, but only those with TRAb (n=3) developed AITD. The OR for AITD was 1.51 given TRAb compared to those with no TRAb at baseline. At 24 months, 27 patients were positive for either of the thyroid Ab, 93% (25/27) of these developed AITD. In contrast, only, 30% (15/51) of those thyroid Ab negative developed AITD (p<0.0001 x2- test).
AITD was developed in 40% of ALZ treated patients, at 24 months 21% had AITD which was similar with that reported from the pivotal studies of ALZ. Thyroid Ab preceded AITD in 62 % of cases. In contrast, the risk of AITD was low in cases without thyroid Ab. Although, monitoring thyroid Ab may be useful identifying patients at high risk for AITD, this has not so far had any therapeutic incentives.