Inflammatory Myositis – Thinking Outside the Box

A huge part of rheumatology is pattern recognition. But what happens when a patient falls outside of a conventional disease presentation? Moreover, when a rare disease, such as myositis, is the diagnosis in question, things can get very confusing. While the inflammatory myopathies have loosely been categorized in the past as dermatomyositis, polymyositis, or autoimmune necrotizing myopathy, it is being increasingly recognized that myositis patients don't always fit into these categories. With the discovery of myositis specific autoantibodies, our thinking regarding categorizing patients with myositis is shifting.

As an example of this, Dr. Myma Al-Bayda and her colleagues (poster, abstract #299) at Johns Hopkins University have presented a phenotype of patients with the NXP-2 antibody who presented with subcutaneous edema, distal weakness and dysphagia. This phenotype is unique in that distal weakness is observed; for inflammatory myositis patients, the general rule of thumb is that only proximal weakness is seen. Moreover, subcutaneous edema is an unusual manifestation of myositis; we are all familiar with a heliotrope rash or Gottron's papules, but edema is something outside of the box. In addition, these patients may present with pain; although the general mantra for myositis is that pain is rarely seen, this is clearly not the case with all patients!

So what is NXP-2 autoantibody? It is also known as anti-MJ. It is a myositis specific autoantibody. It is often associated with juvenile dermatomyositis, and in adults can be associated with calcinosis as well as underlying malignancy.

Dr. Al-Bayda and her colleagues performed a restrospective chart review on patients seen at the Johns Hopkins Myositis Centre between 2002-2015. They identified patients with dermatomyositis, either by fulfilling the conventional Bohan and Peter criteria or through muscle biopsy findings. Patients had autoantibody testing for a wide panel of myositis specific autoantibodies, and 40/120 patients tested positive for NXP-2. These patients had more significant findings of subcutaneous edema, as well as dysphagia, compared to NXP-2 negative patients, with a trend towards having more dysphagia.

So the next time you see a patient with edema, generalized weakness and dysphagia, consider a myositis diagnosis in your differential. For a rare, uncommon disease, there are certainly many possibilities for additional discovery in the future – and with the recognition of different phenotypes, perhaps this disease is not as rare as we think!

More reports from ACR 2015