Background/Purpose: Although HP Acthar gel is a purified, injectable formulation of full-length adrenocorticotropic hormone approved by the FDA for use in myositis, peer-reviewed data is limited. We report long-term outcomes of myositis patients after 6 months of Acthar gel in an open-label pilot study.

Methods: Refractory myositis patients (6 DM, 4 PM) completing 6 months of treatment were included in the study. At the end of trial, 7 of 10 patients met criteria for response at 6 months with a significant reduction in prednisone dose. Post-trial follow-up period was 6 months with assessments at every 2 months which included collection of myositis core set measures (CSM) of disease activity [i.e. extra-muscular global disease activity (Ex-Musc global), physician global disease activity (MD-global), patient global disease activity (Pt-global), health assessment questionnaire (HAQ-DI), manual muscle testing (MMT), and muscle enzymes]. Treatment during the post-trial period was standard of care by the treating physician. ACR-EULAR myositis response criteria as well as the IMACS definition of improvement (DOI) were used to evaluate 12-month outcomes.

Results: 2 of 10 patients were lost to follow-up and 8 patients completed 6 months of post-trial visits. All patients continued their baseline immunosuppressive drugs and were off Acthar gel at the end of trial. Following discontinuation of Acthar gel, all patients had a slow clinical decline with an average time to flare of 4.3 months (median 5, range 0.5-7). Fifty percent of patients (n=4) were restarted on Acthar after an average of 10.3 months (6-13 months) with no other change in medications. The remaining patients who flared were managed by increasing prednisone doses. Patients had an average 41% increase in Ex-Musc global (median 20%, range 0-127%), 79% increase in MD-global (median 107%, range -100%- 166%), 7% increase in HAQ-DI (median 0%, range -62% -576%), 0.6% increase in Pt-global (median 0%, range 16%- 17%), and 3% decrease in MMT (median: -0.7%, range: -11 -4%) 6 months after Acthar discontinuation. Among 4 patients who restarted Acthar, one was lost to follow-up and 2 showed a partial clinical response in muscle strength and rash after 2 and 3 months and were subsequently treated with IVIG. One patient showed a complete response after restarting Acthar with increased muscle strength and rash resolution. Adverse events with Acthar use included dizziness, facial puffiness and upper respiratory tract infection.

Conclusion: Patients discontinuing Acthar after 6 months of clinical efficacy demonstrated a slow increase in disease activity, disability index, and decrease in muscle strength and had their first flare at 4 months after study drug discontinuation. There is need for a randomized, double-blind, placebo-controlled, clinical trial of Acthar in myositis patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/long-term-follow-up-results-of-myositis-patients-treated-with-h-p-acthar-gel/