An Extension Study for Participants Who Have Completed the Treatment Period of a Qualifying Parent Study

An Adverse Event (AE) was any untoward medical occurrence in a participant or clinical study participant, temporally associated with the use of study intervention, whether or not considered related to the study intervention. An AE was considered treatment emergent relative to a given treatment if the event occurred for the first time during the effective duration of treatment and was not seen prior to the start of treatment, or the event was seen prior to the start of treatment but increased in severity during treatment. AEs included both serious adverse events (SAEs) and all non-SAEs.

Hematology laboratory parameters: hemoglobin (grams per deciliter [g/dL]); hematocrit (percentage [%]); lymphocytes (10^3 per (/) millimeter[mm]^3); lymphocytes/leukocytes (%); neutrophils (10^3/mm^3) less than (<)0.8*lower limit of normal (LLN), leukocytes (10^3/mm^3) <0.6*LLN, neutrophils (10^3/mm^3); basophils (10^3/mm^3); basophils/leukocytes (%); monocytes/leukocytes (%); activated partial thromboplastin time (seconds [sec]); prothrombin time (sec) more than (>)1.2*upper limit of normal (ULN). Clinical chemistry: potassium (milliequivalents per liter [mEq/L]); bicarbonate (mEq/L) <0.9*LLN, creatine kinase (units per liter [U/L]) >2.0*ULN, glucose (milligram per deciliter [mg/dl]); glucose-fasting (mg/dl) >1.5*ULN. Urinalysis: Urine glucose; ketones; urine protein; urine hemoglobin; nitrite; leukocyte esterase; hyaline casts (1/per leukocytosis promoting factor (more than or equal to [>=] 1, urine erythrocytes (scalar); urine leukocytes (scalar) >=20.

Vital signs included the following parameters: sitting diastolic blood pressure (millimetres of mercury [mmHg]) change >=20 mmHg increase; sitting systolic blood pressure (mmHg) change >=30 mmHg increase, sitting diastolic blood pressure (mmHg) change >=20 mmHg decrease and sitting systolic blood pressure (mmHg) change >=30 mmHg decrease.

ECG parameters evaluated were: PR interval value >=300 milliseconds (msec); QRS duration value >=200 msec; QT interval value >=500 msec; corrected QT Interval using Fridericia's formula (QTCF) 450 less than or equal to (<=) value <480 msec, 480 <=value<500 msec and value>=500 msec.

CDASI is a validated DM-specific instrument designed to systematically quantify the extent of cutaneous disease. Disease involvement in 15 different anatomical locations was rated using three activity (erythema, scale, erosion/ulceration) and two damage (poikiloderma, calcinosis) measures. The presence and severity of Gottron's papules, periungual changes and alopecia were also captured. Total CDASI activity score was based on the physician's evaluation of three activities (erythema, scale, erosion/ulceration), presence and severity of Gottron's papules, periungual changes and alopecia. Total CDASI activity score ranged from 0 to 100, where higher scores indicated higher levels of disability.

CDASI is a validated DM-specific instrument designed to systematically quantify the extent of cutaneous disease. Disease involvement in 15 different anatomical locations was rated using three activity (erythema, scale, erosion/ulceration) and two damage (poikiloderma, calcinosis) measures. The presence and severity of Gottron's papules, periungual changes and alopecia were also captured. Total CDASI activity score was based on the physician's evaluation of three activities (erythema, scale, erosion/ulceration), presence and severity of Gottron's papules, periungual changes and alopecia. Total CDASI activity score ranged from 0 to 100, where higher scores indicated higher levels of disability.

CDASI is a validated DM-specific instrument designed to systematically quantify the extent of cutaneous disease. Disease involvement in 15 different anatomical locations was rated using three activity (erythema, scale, erosion/ulceration) and two damage (poikiloderma, calcinosis) measures. The presence and severity of Gottron's papules, periungual changes and alopecia were also captured. Total CDASI activity score was based on the physician's evaluation of three activities (erythema, scale, erosion/ulceration), presence and severity of Gottron's papules, periungual changes and alopecia. Total CDASI activity score ranged from 0 to 100, where higher scores indicated higher levels of disability.

CDASI is a validated DM-specific instrument designed to systematically quantify the extent of cutaneous disease. Disease involvement in 15 different anatomical locations was rated using three activity (erythema, scale, erosion/ulceration) and two damage (poikiloderma, calcinosis) measures. The presence and severity of Gottron's papules, periungual changes and alopecia were also captured. Total CDASI damage score was based on the physician's evaluation of two damage (poikiloderma, calcinosis) measures, and presence and severity of Gottron's papules. Total CDASI damage score ranged from 0 to 32, where higher scores indicated higher level of skin damage.

CDASI is a validated DM-specific instrument designed to systematically quantify the extent of cutaneous disease. Disease involvement in 15 different anatomical locations was rated using three activity (erythema, scale, erosion/ulceration) and two damage (poikiloderma, calcinosis) measures. The presence and severity of Gottron's papules, periungual changes and alopecia were also captured. Total CDASI damage score was based on the physician's evaluation of two damage (poikiloderma, calcinosis) measures, and presence and severity of Gottron's papules. Total CDASI damage score ranged from 0 to 32, where higher scores indicated higher level of skin damage.

There are 6 core set measure that comprised of TIS: 1) Physician Global Assessment Score [PhGA] (from Myositis Disease Activity Assessment Tool [MDAAT], 0-100 mm or 0-10 centimeter (cm) on visual analogue scale [VAS], higher scores= worse health status); 2) Patient Global Assessment Score [PtGA] (0-100 mm or 0-10 cm on VAS, higher scores= worse status); 3) Manual Muscle Testing-8 (MMT-8) designated muscle groups (0-80, lower scores= higher level of disability); 4) Health Assessment Questionnaire Disability Index [HAQ-DI] (0-3, higher scores= worse status); 5) Global Extramuscular Disease Activity (from MDAAT, 0-10 cm on a VAS, higher scores= higher level of disability); 6) Participant's most elevated muscle enzymes. TIS was sum of all 6 improvement scores associated with the change in each core set measure. TIS ranged from 0 to 100; where TIS>=20 shows minimal improvement, TIS >=40 shows moderate improvement and TIS >= 60 shows major improvement.

PhGA: Investigator was asked to evaluate the participant's overall disease activity on a VAS of 0 cm (very good) to 10 cm (very poor), higher scores indicated worse health status.

PtGA was the assessment of the severity of disease by the participant/participant's guardian, using a VAS from 0 mm (no evidence of disease activity) to 100 mm (extremely active or severe disease activity). Higher score indicated worse status.

MMT-8 is a tool that assesses muscle strength using manual muscle testing. Eight designated muscles are tested unilaterally with a total potential summed score of 0-80. Lower scores indicated a higher level of disability.

HAQ-DI consisted of eight sections (including dressing & grooming, arising, eating, walking, hygiene, grip, reach, and activities). Each section had multiple questions that the participant used to rank their functionality and ranged from 0 to 3 where 0 = without any difficulty and 3 = unable to do. For each participant, the average ranking was calculated for each of the eight sections. HAQ-DI had a score range of 0 to 3, where higher score reflected worse status.

Creatine kinase is a muscle enzyme measured in units per liter (U/L).

MDAAT tool measures the degree of disease activity of extramuscular organ systems and muscle on a VAS of 0 to 10 cm, higher scores indicated higher level of disability.