Muscle Disorders

Last post of the semester! This one shouldn't be too long because we didn't really have a lot of time to cover this topic.

Describe the characteristics of Muscular Dystrophy. Identify the differences between the Duchenne and Myotonic forms of the disease. What is Gower's manoeuvre?

Muscular dystrophy is a genetic muscular disorder in which dystrophin is defective. This can lead to muscle weakness and even breakdown of muscle tissue to be replaced by fat and connective tissue. (I've posted some pictures of mouse tissue with this disease here.)

One of the more severe types of muscular dystrophy is Duchenne's muscular dystrophy. It is an X-linked recessive disorder, so it is more common in males. It has an early onset and rapidly progresses, so that patients are often wheelchair-bound in their teens and eventually die of respiratory failure due to the breakdown of respiratory muscles.

Another type of muscular dystrophy is the myotonic variety, in which muscle relaxation is delayed. This is also genetic, but it is autosomal dominant. It progresses more slowly than the Duchenne variety.

Other general characteristics of muscular dystrophy include cardiomyopathy (disease affecting the heart muscle), increased creatine kinase (an enzyme common in muscle cells that is released when they die), vertebral deformities such as scoliosis, and Gower's manoeuvre. Gower's manoeuvre is a result of patients being too weak to stand easily, which often occurs as pelvic muscles are usually the first to be affected by this disease. Essentially, patients will use their hands to push themselves up, walking their hands up their legs as they do so.

What is the cause of Myasthenia Gravis? What are its symptoms? How is it diagnosed? (Note: This disorder is not on the exam, but I'm going to include it for completeness.)

I've already mentioned myasthenia gravis in a post for Immunology, but I'm going to flesh it out with some more details. Myasthenia gravis, which is more common in females, causes muscle weakness, initially in the face. This causes stuff such as diplopia, ptosis, facial droop and difficulty swallowing. Stress or alcohol may induce a myasthenia crisis, where breathing is affected.

Tests for myasthenia gravis include looking for antibodies against ACh, EMG (electromyography- recording the electrical activity produced by muscles) and looking for a response to AChE (acetylcholinesterase) inhibitors. Acetylcholinesterase is an enzyme that breaks down acetylcholine, and when it is inhibited, that leaves more acetylcholine to stimulate the relatively low number of ACh receptors in patients with the disease. Patients can experience dramatic improvements with these.

Treatment includes the aforementioned AChE inhibitors, thymectomy (thymus hyperplasia is often associated with this disease), immunosuppressants and plasmapheresis. Plasmapheresis is a technique in which plasma is removed, antibodies against ACh are removed from the plasma, and the plasma is returned to the patient.

And that's my last post for the semester! Good luck for finals!