Pathogen Myositis with Trichinella – Infectious Myopathies

00:00 Now let's shift gears and think of what other pathogens can cause infection of the muscle.

00:06 This is extremely uncommon, but we do see muscle infection in the setting of systemic infection or in certain conditions that affect specifically the muscle. Let's think about viruses. Certain viruses can affect the muscles. Influenza is a common one. One of the early symptoms with influenza is myalgias and muscle pain, and this is a result of some muscle irritation and inflammation in the setting of acute influenza. Coxsackieviruses and various arboviruses can also affect the muscle in their disease course. Rarely, we'll see bacterial infections that involve the muscle. Lyme disease associated myositis and borrelia associated myositis are 2 that can be seen. And then there are a number of parasites that can encyst in and infect the muscle. Toxo, trypanosoma, and several others including trichinella and we're going to focus on trichinella. It's not something that you may see, but it is a very interesting presentation and sometimes shows up on board exams because it's a little bit different than our typical myopathic presentation and something I'd like for you to be familiar with. So let's look at the life cycle of trichinella and understand how trichinella causes disease or trichinellosis. This starts with wild or domestic animals and we'll talk about the life cycle in wild and domestic animals first and then move to what happens with humans. So first, the animal ingests encysted larvae of the trichinella. Second, the larvae are released in the stomach and mature and at this point in time the animal or human may present with diarrhea, gastrointestinal irritation, mild cramping, GI complaints. Those encysted larvae can enter the lymph system or the blood vessels and circulate throughout the system and lodge in the skeletal muscle as well as other areas. And here we can see periorbital edema, fever, eosinophilia from the systemic reaction to this and occasionally CNS symptoms. In the muscle when these larvae encyst in the muscle, they can enter skeletal muscle as well as some myocardial muscle, but primarily we see skeletal muscle invasion. In the skeletal muscle, this nurse cell L1 complex matures and that takes about 20 days and ultimately we see the normal and calcified nurse cell larvae complexes, inflame the muscle, and cause degeneration, inflammation, and weakness.

02:32 So let's look at what happens in the human. Humans ingest the encysted larvae from striated muscle and this may be through uncooked or undercooked meat or animals or other ingestion.

02:45 The larvae are released into the small intestines. In the intestines they mature into adults in the small intestines. The larvae are deposited into the gastrointestinal mucosa and there they can enter either lymph drainage or the systemic circulation through the blood vessels.

03:03 We see that as a result of circulation, the larvae can lodge or encyst in the liver or various striated muscles and lead to muscle and other organ dysfunction. The same life cycle we saw in the pig and other animals. What about disease? How does trichinella cause disease and what are the stages of the disease that we see? As you see, trichinellosis may progress from the intestinal phase to the systemic phase with muscle involvement and different symptoms can be present at each phase. In the intestinal phase after the larvae are ingested, we see diarrhea, abdominal cramping, and gastrointestinal symptoms, and constipation, some usually lasting about 2-7 days in this phase of the disease. As the larvae enter the lymph drainage and the systemic circulation and encyst in muscles, we begin to see weakness, myalgias is extremely common and we can see CNS involvement, cardiac muscle can be affected, pulmonary system can be affected wherever the larvae may encyst. In the muscle phase which is specific to this infection, we see that affected muscles are those with increased blood flow and importantly we can see involvement of the orofacial muscles. This is predominant in this condition. We see involvement of extraocular muscles, the masseter muscles, the larynx, the tongue, the neck muscles, the diaphragm, intercostals, limb flexors, a number of those proximal and bulbar predominant muscles are involved. So these patients present with prominent bulbar weakness that progresses throughout their circulation and generalized weakness then follows. And this is often 2-7 days after gastrointestinal symptoms, diarrhea, and constipation. What's the workup for a trichinosis myositis? A CBC may show leukocytosis because this is an infection and because it's a parasite we may see eosinophilia.

05:03 Eosinophilia is a good tip off that we may be dealing with a parasitic process. CK is elevated typically somewhere between the thousands and often not up to the 10,000's but with vigorous disease we can see significantly elevated CKs. This can be associated with increase in the CKMB. Recall that this isoenzyme, this iso form of CK is the myocardial form. This larvae can encyst within the myocardium and we can see increase in myocardial specific CK. How do we manage these patients? Mild cases are managed supportively with analgesia and antipyretics and other supportive care fluids. Severe cases may require antiparasitic agents.

05:46 Mebendazole and albendazole are 2 of those that may be considered. And we may not treat chronic inflammation from muscle disease in selected patients.