Background/Purpose: Idiopathic Inflammatory Myopathies (IIM) remain a major clinical challenge worldwide. The precise aetiopathogenesis of this chronic and disabling disorder remains elusive which precludes the development of novel and effective therapeutic strategies. The most visible consequence of this lack of effective therapies is the damage caused to these patients with the consequent decrease in quality of life, high morbidity and mortality. The complexity of managing these diseases is even higher because of the vast comorbidities affecting these patients.

Methods: Retrospective review of the cohort of patients followed in a dedicated unit of a tertiary hospital, with special incidence in damage and comorbidities, between January 2008 and December 2018. Damage was assessed by Myositis Damage Index (MDI) score. Comorbidities were scored according to Charlson Comorbidity Index in the last year of the study (2018).

Results: Ninety four patients were included, 79 women and 15 men, with a medium age at diagnosis of 46 years-old and a medium follow-up of 12 years. Paraneoplastic myopathies accounted for 20.2% of the cases and overlap myopathies were present in 19.1%. A definitive diagnosis was obtained in 37.2% of patients, according to Bohan and Peter criteria and 42.6% according to ACR/EULAR classification criteria. Only 8.5% of patients were documented in sustained remission without drugs. Damage scores were calculated as a whole and individually for the 11 dimensions of MDI score. Only 13.8% of the patients presented with MDI score of zero, meaning that more than 86% presented with some kind of damage. The majority of this was cardiovascular damage, along with its end-organ consequences, and psichiatric. Mortality occurred in 17% of patients with a medium age of 65 years-old and the most common cause was malignancy. Average MDI extent was 5.56 (range: 0-38) but average MDI severity was 87.6 (range: 0-110). Comorbidities were present in 90.5% of patients and essentially overlap with damage as they are mainly its consequence and so the most common are also cardiovascular risk and secondary organic diseases. Average Charlson Comorbidity Index was 4.6 predicting an average survival at 10 years of 52%. Of note, almost 10% of patients present with immunodeficiency unrelated to immunosuppressive therapy, mainly humoral.

Conclusion: Damage is high in IIM patients and is mainly cardiovascular, as opposed to muscle/ cutaneous damage. This appears essentially the result of the therapy used to control the disease, particularly prolonged systemic steroids, and persistent inflammation in refractory patients. A better knowledge of the disease physiopathology is essential for an improvement of its therapeutic strategies, particularly aiming steroid-free regimens. 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/damage-and-comorbidities-in-a-cohort-of-patients-with-idiopathic-inflammatory-myopathy/