Pearl #2 was to bear in mind that many immunosuppressive medications may need to be renally dosed in patients with impaired renal function. Dr. Chung pointed out that more than 600 drugs have a high risk for toxicity in patients with impaired renal function, and rheumatologists should bear in mind that baricitinib, tofacitinib, methotrexate, leflunomide, cyclophosphamide and sulfasalazine may have specific issues arise in patients with reduced GFR. In a study from Muanda et al., adults with chronic kidney disease who started low-dose methotrexate (5–35 mg per week) had a higher 90-day risk of serious adverse events, such as a hospital visit with myelosuppression, sepsis, pneumotoxic effects or hepatotoxic effects, compared with those who started hydroxychloroquine (200–400 mg per day).15
Pearl #3 was that clinicians must not ignore the possible injurious effects of drug interactions. Dr. Chung provided a case example of a patient on tizanidine, a medication that is extensively metabolized in the liver by the cytochrome P450 1A2 (CYP1A2) enzyme. When CYP1A2 activity is reduced, as is the case with patients taking strong CYP1A2 inhibitors like fluvoxamine or ciprofloxacin, the metabolism and clearance of tizanidine are markedly decreased. This can result in substantially higher serum concentrations of the drug and increased risk of adverse effects like hypotension and excessive sedation. Similarly, rheumatologists must remember that for patients on allopurinol co-administration of azathioprine is dangerous as a highly significant interaction between the drugs can cause life-threatening bone marrow suppression.
Potential Mimics of Inflammatory Myopathies
The fourth talk of the session was from Jens Schmidt, MD, FEAN, FAAN, chair of the Department of Neurology and Pain Treatment, Immanuel Klinik Rüdersdorf, University Hospital of the Brandenburg Medical School Theodor Fontane in Rüdersdorf/Berlin, Germany, who described the potential mimics of the inflammatory myopathies. Dr. Schmidt provided the audience with an excellent online resource from the Neuromuscular Disease Center at Washington University in St. Louis; he noted that this site is continually updated and, thus, quite helpful to clinicians.16 Dr. Schmidt explained that a fundamental issue in the field is the confusing terminology in myositis that is not uniform across the world or even among professional societies. Given the diversity of terms and acronyms to describe the forms of these conditions, it can be hard for clinicians to speak the same language with one another. For example, some feel that the term polymyositis should be discarded into the wastebasket of history, but Dr. Schmidt explained it may still be needed to describe certain patients whose muscle disease cannot be described by an alternative diagnosis. Some have argued that scleromyositis should be recognized within both the systemic sclerosis and the autoimmune myositis spectrum of diseases, but this is not a universally accepted term.17
