1203: Rituximab in Treatment Refractory vs Treatment Naive Anti Signal Recognition Particle (SRP) Myositis A Case Series

Background/Purpose: Anti-Signal Recognition Particle (Anti-SRP) Myositis is a form of Polymyositis. Available consensus guidelines recommend initial combination therapy of high dose corticosteroids and Methotrexate and addition of Rituximab (RTX) within 6 months of starting therapy.

Methods:

Objectives:

1. Comparison of non-rituximab vs Rituximab therapy in treatment naïve

Anti-SRP Myositis patients.

2. Comparison of Rituximab in Treatment refractory vs Treatment naïve

anti-SRP Myositis patients.


Methods:

It is a Single centre retrospective study. Patients satisfying EULAR/ACR

classification criteria for Idiopathic Inflammatory Myopathy AND anti-SRP

antibody in moderate to high titer were defined as cases. Patients with

concomitant presence of any other Myositis specific antibody (MSA) in

moderate to high titer were excluded. Complete remission (CR) was defined as

MMT increase of

≥ 20% 𝑓𝑟𝑜𝑚 𝑏𝑎𝑠𝑒𝑙𝑖𝑛𝑒 𝑖𝑛 𝑀𝑎𝑛𝑢𝑎𝑙 𝑀𝑢𝑠𝑐𝑙𝑒 𝑡𝑒𝑠𝑡𝑖𝑛𝑔 (𝑀𝑀𝑇 ― 8) AND

normalisation of CPK while partial remission was defined as

≥ 20% 𝑖𝑛𝑐𝑟𝑒𝑎𝑠𝑒 𝑖𝑛 𝑀𝑀𝑇 ― 8 but elevated CPK ( >2 times of ULN). Patient

with ≥ 20% worsening in MMT from highest value and/or > 3 times increase

in CPK from lowest value while on standard of care therapy were defined as

refractory cases.

Results: A total of 13 patients of SRP Myositis were included. Out of 13 cases-8 cases

initially received Immunosuppressants other than Rituximab (defined as initial

non-rituximab therapy group) while 5 cases initially received Rituximab

(defined as initial Rituximab Therapy group). In initial non-rituximab therapy

group, 3 received Methotrexate, 2 received monthly Cyclophosphamide

therapy for 6 months, 2 received Mycophenolate Mofetil and 1 received

Azathioprine. All 8 cases relapsed after Complete or partial remission during

follow-up and met the criteria of refractory disease. Refractory patients

received Inj. Rituximab 1 gm two doses. In initial Rituximab therapy group cases

received Rituximab 1 gm two doses and did not receive any other conventional

DMARD (C-DMARDs).

Conclusion:
1. Complete remission (CR) at 6 months is higher in initial rituximab therapy

group in treatment naïve anti-SRP Myositis patients. However, both

groups showed similar improvement in MMT-8, reduction in CPK, and

corticosteroid dose reduction at 6 months after starting therapy.

2. RTX therapy is equally effective at 6 months in treatment refractory and

treatment naïve patients in terms of improvement in MMT and reduction

in CPK. Treatment-naïve patients had significantly greater corticosteroid

needs throughout the treatment period.