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.