Overlap Myopathies

00:00 Now, let's talk about the last type of inflammatory myopathy. Overlap myopathies. And this is where there is an underlying myopathy that overlaps with some other systemic condition.

00:13 The patient may have pulmonary symptoms or may have rheumatologic symptoms, or connective tissue disorder, it's myopathy plus something else. For poly, dermato, inclusion body, and necrotizing myopathies, the primary problem is in the muscle and there is no other organ system that's involved. It's a primary muscle inflammation. In overlap myopathies, the primary problem is actually the immune mediated auto-immune condition. It's the rheumatologic condition or the pulmonary condition and we are happening to see muscle involvement. So let's walk through how those patients present. The onset is typically sub-acute so over weeks to months. And again, patients present with a myopathy. The distribution is symmetric, painless, proximal weakness, normal sensory findings, and normal reflexes. The patients have a typical myopathy. But in addition to the myopathy, we also see other associated findings. Frequently, we see these patients suffer from a mix connective tissue disorder. Systemic sclerosis, lupus, some other non-specific mix connective tissue disorder, rheumatoid arthritis or Sjogren’s. And here, we're seeing overlap of that condition with involvement in the muscle. So let's think more about how we approach these patients.

01:38 Some patients will present with primary muscle findings, they will have an idiopathic inflammatory myopathy. They will present with proximal, progressive, symmetric weakness with no sensory findings and normal reflexes and they have a myopathy. Other patients will present with a mix connective tissue disorder, problem with rheumatoid arthritis, lupus or Sjogren’s. And what we want to look for in those patients is the presence of an underlying antibody that's causing both the systemic auto-immunity and the muscle inflammation. Some of those include antisynthetase antibody syndrome. And this is a syndrome where patients develop a myopathy and you can see on the blue here it's a proximal predominant myopathy but patients can have some hand weakness and in addition they also have lung involvement, interstitial fibrosis of the lungs, and problems with breathing and pulmonary symptoms. This is associated with a specific antibody called anti-Jo-1. And in these patients we test for anti-Jo-1 and when we see those antibodies, that's the classic triad for antisynthetase antibody syndrome. The second is anti-SRP or signal recognition protein syndrome. This again is a myopathy, though it tends to be a more diffuse myopathy as you see here in the yellow, involving both proximal and distal muscles and this is an acute onset necrotizing myopathy.

03:03 Patients present suddenly with fulminant weakness, elevated CKs, and this is a prominent acute presentation. The last antibody that we can see associated with these syndromes is anti-Mi-2 and you can see here it also follows that typical proximal distribution. And any of these conditions can be associated with a rheumatologic disorder, a connective tissue disorder and that tips us off that this may be an overlap myositis.