Necrotizing Autoimmune Myositis

00:00 Now, let's move to the fourth type of inflammatory myopathy. Necrotizing autoimmune myositis. And this is a really important condition. It is increasingly described. We are increasingly seeing this in patients. And many patients who we once thought had polymyositis we're discovering, may actually have necrotizing autoimmune myositis. This condition is associated with viral infections. Certain viral infections set off the immune system to injure and kill and damage muscles leading to rapid necrosis. It's associated with certain types of cancer and paraneoplastic conditions, as well as auto-immune diseases like lupus and Sjogren’s and other autoimmune conditions. And importantly, this condition has been described with certain medications. Medications that may unearth previously undiagnosed autoimmune condition like HMGCoA reductase antibody syndrome. And we'll talk more about that and that will be the prototypical syndrome that we need to associate with necrotizing autoimmune myositis. So, how does this present? How was it similar and different from poly, dermato and inclusion body myositis? Well, it's onset can be sub-acute. But patients can also present acutely with weakness that rapidly develops over the course of days. A fulminant presentation of weakness which is much different from the other conditions that we have talked about. Typically, the distribution is symmetric, it's painless and it's proximal. So it follows that typical pattern of what we see with the muscle disorder. There's an absence of sensory changes and reflexes are normal. It's fitting that myopathy pattern and what we see, as you can see here on the image to the right as we see necrosis of muscle fibers. The reddish pink fibers or the muscle and that light pink is areas of necrosis. Death of muscle which leads to prominent inflammation which we're going to see in this condition. So, what's our work up? Well again, we're looking for an inflammatory myopathy so we're going to look for signs of inflammation by testing the CK. And CK elevations tend to be much higher than what we see with poly, dermato and inclusion body myositis. There is vigorous inflammation in and around the muscles and we see release of CK, it levels higher than we see with other inflammatory myopathies. The EMG still shows a myopathic pattern, short duration, small amplitude, muscle contraction, muscle fiber, muscle firing, and often with spontaneous activity indicating that there's inflammation around the muscle, impairing transmission at the neuromuscular junction. Muscle biopsy shows muscle necrosis and can be important in the evaluation but is not required and we must exclude other causes. Management has typically similar to poly and dermatomyositis. We use corticosteroids and typically prednisone. This is also an immune mediated condition, and we want to lessen, quiet, calm the immune response and we use prednisone as a corticosteroid. So let's talk about a test case of a patient presenting with necrotizing autoimmune myositis. And this is important. I want you to understand this. You may see this in the clinic when evaluating patients or see a clinical vignette on this. So this is an adult patient who recently was started on a statin medication for cholesterol lowering and who develops myopathic weakness, proximal weakness, normal sensory findings, normal reflexes over the course of several weeks. This can happen early after starting the statin or late after having been on a statin medicine for some time. It's idiosyncratic. It can happen at any point in the treatment course. For that patient, we're worried this could be inflammation and so we test the CK and see that the CK is elevated, indicating muscle inflammation. Our first step is to rule out that this is from the statin. This could be a toxic myopathy. So, the first step in management is to stop the statin. And in many of these patients we will see that over the next 4 to 6 weeks, the CK level will decline, the weakness will go away, and the patient will go back to normal. Normal strength, no signs of muscle inflammation. And in that situation, the patient is suffering or has suffered from a toxic myopathy from the statin. But in some patients that is not what happens. 4 to 6 weeks down the road, we still see that the CK is elevated or may even be higher. The patient still has weakness and sometimes that weakness is worsening. And in those cases, we're not dealing with the toxin-induced myopathy but something different, an autoimmune myopathy.

04:35 Necrotizing myopathy from HMGCoA reductase antibodies. And what we think is going on here is that that statin medicine has unearth and underlying autoimmune condition. This patient is susceptible to developing auto-reactive antibodies or this HMACoA reductase antibodies. And in those situations it's not the statin that is driving the muscle damage, but this HMGCoA reductase antibodies. Those patients require longer term treatment.

05:05 Immunomodulation in addition to simply withdrawal of the statin medication. This is an important thing to recognize and we'll talk more about HMGCoA reductase mediated myopathy, in a subsequent lecture.