Background Knowledge of cardiac involvement in idiopathic inflammatory myopathies (IIM) is limited and a matter of debate with reported frequencies between 6% and 75%. Although clinically overt disease is rare, cardiac events are the major cause of death in IIM. No studies of the heart by SPECT/CT in newly diagnosed, untreated adults with IIM have been performed.

Objectives To examine cardiac involvement in newly diagnosed, untreated patients with IIM by cardiac SPECT/CT imaging compared to a gender- and age- matched control group.

Methods In a cross-sectional, single-centre study of 14 untreated patients newly diagnosed with IIM (polymyositis 7, dermatomyositis 4, cancer-associated myositis 2, immune-mediated necrotizing myopathy 1) and of 14 gender- and age- matched healthy controls. ^99mtechnetium pyrophosphate (^99mTc-PYP) SPECT/CT imaging was performed and cardiac ^99mTc-PYP uptake was correlated to blood ^99mTc-PYP uptake and weight-adjusted. Cardiac ^99mTc-PYP uptake was reported in kBq/ml with the following ranges; low uptake (< 0 kBq/ml); normal uptake (0-12 kBq/ml); or high uptake (≥ 12 kBq/ml). Furthermore, disease activity was measured by Health Assessment Questionnaire (HAQ, range 0-3), myositis intention-to-treat activity index (MITAX, range 0-1), manual muscle test of 8 muscle groups (MMT8, range 0-80), serum levels of creatinine kinase (CK), C-reactive protein (CRP) and cardiac troponin I (TnI), a highly specific marker of myocardial injury. Also presence of circulating antinuclear antibodies (ANA) and myositis specific autoantibodies (MSA) was determined.

Results The mean age of the patients was 59.5 years and 57% were women. Mean duration of disease symptoms was 2 years (range 0.1-10.1). At disease onset 14% had mild, 43% had moderate and 43% patients had severe or extremely severe myositis. At study entry mean HAQ was 1.2 (range 0.25 – 3), mean MITAX was 0.42 (range 0.17 -0.72), and mean MMT8 was 69 (range 52 – 80). Increased CRP levels was found in 6 (43%) patients and 12 (86%) had elevated levels of CK. ANA was found in 6 patients and 5 patients had one or more MSA. TnI was insignificantly increased in IIM compared to healthy controls (P < 0.05). Abnormal cardiac ^99mTc-PYP uptake was observed in 7 (50%) patients and no controls (P = 0.002).

Conclusions Heart involvement, as detected by the presence of abnormal cardiac ^99mTc-PYP uptake on SPECT/CT imaging, is more prevalent in untreated IIM patients than in age- and gender- matched healthy controls. These findings support the notion that heart involvement in IIM patients is common and that a comprehensive heart evaluation in IIM patients at disease onset is warranted.

Disclosure of Interest None Declared