Intravenous immunoglobulin (IVIG) is commonly used in the treatment of idiopathic inflammatory myopathies (IIM). However, IVIG is not licensed for the treatment of IIM in Canada. Moreover, there is a paucity of evidence concerning its use. There are many case reports, as well as "expert opinion" that supports the use of IVIG for the treatment of refractory IIM, IIM associated with dysphagia and respiratory muscle weakness as well as overall severe weakness, and refractory skin findings of dermatomyositis. We undertook this study (abstract 219) to document how Canadian physicians use IVIG for the treatment of IIM.
In order to do this, we developed a survey to address various aspects of IVIG use for IIM, with input from a core team of rheumatologists, neurologists and patient representatives for content and validity. Members of the Canadian Rheumatology Association, as well as the Canadian Inflammatory Myopathy Study and a Canadian network of neuromuscular physicians, were invited to participate by an email containing a link to a web-based survey. Descriptive statistics were used to summarize the data.
Over 573 physicians received the survey, and 166 participated; of these, 155 confirmed that they treat IIM. The majority were rheumatologists (79.9%), and 18.2% were neurologists. The median duration of practice was 15 years. The majority of patients were seen in an academic setting. Most physicians had 1-10 prevalent cases of IIM currently in their practice. Interestingly, physicians who used IVIG generally did so in less than 25% of their IIM patients, and 15% reported they didn't use it due to access problems or preference to refer to other physicians. Other reasons for not using IVIG included belief in effectiveness of conventional medications, as well as cost issues.
IVIG was mostly used for dermatomyositis (91.1%), but was also used for polymyositis (71.5%), connective tissue disease-related myositis (8.6%), necrotizing autoimmune myositis (34.1%), statin-associated HMGCR antibody necrotizing myopathy (23.6%), cancer-associated myositis (22.8%) and inclusion body myositis (5.7%). The most common indications for IVIG were rapidly progressive muscle weakness (78%), diaphragmatic weakness (57.4%) and dysphagia (45.5%). IVIG was also used for cardiac disease, moderate/severe skin disease and interstitial lung disease. When used, IVIG was rarely used first-line, and was most often used in combination with glucocorticoids and DMARDs or DMARDs alone (22.4%), and often (48.2%) after failure of combination therapy. Most physicians reported using a dose of 2 gm/kg/month for up to 12 months or until marked improvement. Most found that access to IVIG was readily available (68.8% of respondents).
The results of the survey were predictable in some ways, in that IVIG is commonly used for severe presentations of IIM, including dysphagia and respiratory muscle weakness. However, the results did show that there is wide variation in use of IVIG, and low overall rates of use despite relatively good access to this treatment.
Does this mean we are being good gate-keepers of IVIG? Or perhaps under-treating IIM? Perhaps we should be using IVIG earlier to aggressively combat IIM and shut off inflammation at the onset. However, the cost of IVIG is a definite concern, and this barrier that is not unique to IIM as it is shared with many other "rare" diseases.