Background/Purpose

Recently, idiopathic inflammatory myositis (IIM) has been categorised into distinct subsets based on myositis specific autoantibodies (MSA) and myositis associated autoantibodies (MAA). However, there is little data on prevalence of these autoantibodies from Indian subcontinent. Hence, we studied the prevalence and clinical associations of MSAs and MAAs in Indian patients with IIM.

Methods:

Clinical data and sera were collected from patients with IIM (November 2012-May 2014). Sera were analysed for antibodies against SRP, Mi2, Jo1, PL 7, PL 12, EJ, OJ, Ro 52, Ku, Pm-Scl75 and PM-Scl 100, using line immunoblot assay( Euroimmune).

 Results

During 18 months there were 124 patients with IIM. ANA positivity was found in 84 (68.9%). The distribution of different autoantibodies in different subset is given below:

 

Parameter	DM	PM	CTD assoc. IIM	JDM	Total
Number	55	25	22	22	124
Female: Male	40:15	24:1	22:0	11:11	97:27
Mean age	34.4	35.2	34.4	10.1	30.4
Mean disease duration	8.3+11.2	11.4+16.7	7.6+7	20.6+25.1	10.9
Myosits specific antibodies (number positive)
Mi2	21	2	1	2	26
SRP	3	1	1	1	6
Anti-Jo1	3	6	0	5	14
Other Anti-synthetase	7	3	2	3	15
Myositis associated antibodies (number positive)
Ro52	14	11	15	5	45
Ku	7	1	2	3	13
PM-Scl 100	1	1	2	1	5
PM-Scl 75	3	4	3	3	13
All antibody negative
	13	5	5	10	33

Thirty eight (30.6%) patients had two autoantibodies and 7(5.6%) patients had 3 autoantibodies.

Anti-Jo1 showed positive association(r= 0.31) while anti-Mi2 showed negative association (r= -0.26) with anti-Ro52 antibody. Anti-Mi2 antibodies were strongly associated with adult DM  (p< 0.0001) as well as it was associated with decreased risk for ILD (p=0.001) and increased risk for pharyngeal weakness (p=0.006).   ILD and mechanics hands were strongly associated, both with anti-Jo1and anti-synthetase antibodies (p<0.0001). Four of the six patients with anti-SRP antibody had poor response to multiple drugs. 

Conclusion

Higher prevalence of anti-Mi2 is probably related to higher proportion of patients with DM. We found absence of ILD in patients with anti-Mi2 antibody suggesting that it  may protect against ILD. In Indian population also anti-synthetase antibodies are associated with ILD and anti-SRP with poor response to treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/myositis-specific-and-myositis-associated-autoantibodies-in-indian-patients-with-inflammatory-myositis/