Chapter 27: Skeletal Muscle Part II Flashcards
An 18 year old female comes to your office and presents with a rash over her face, trunk, and upper eyelids. She also complains that she has been having trouble climbing the stairs in her home. On exam you notice bilateral proximal muscle weakness in the lower extremities. During the history, the patient stated that she has previously been diagnosed with Hashimoto’s thyroiditis. At this point you are fairly certain about your diagnosis, but to confirm you decide to take a muscle biopsy. What is your diagnosis, and what pathognomonic feature on biopsy would confirm it?
Dx: Dermatomyositis
Pathognomonic feature: Perifascicular atrophy and immune complexes in capillary walls (even w/o inflammation)
Other classic features include: Positive ANA; PERImysial inflammation (CD4 T-cells); Gottron papules
**Associated w/ increased risk for epithelial cancer (usually lung carcinoma) in middle-aged men
A 36 year old male presents to your office complaining that he has been having trouble swallowing, keeping his head up, and combing his hair. On exam you notice symmetric proximal muscle weakness in the upper extremities, but you do NOT notice any rash. You go ahead and diagnose the patient with polymyositis and tell him you will call him in 3 days once the results of his muscle biopsy are in. What would you expect to see on biopsy to confirm this diagnosis?
Dx: Polymyositis
Biopsy: ENDOmysial inflammation (CD8 T cells) w/ necrotic muscle fibers
*Polymyositis looks much the same as dermatomyositis EXCEPT it does NOT present w/ a rash and it is a cell-mediated (CD8) cytotoxicity disease vs. dermatomyositis which is a CD4/immune mediated microangiopathy disease. Anti-Jo positive.
A 45 year old female presents with general fatigue and the complaint that she is “too tired to eat” (probably wish you came to the last FMSO clinical case discussion now). Upon further interviewing, the patient states that she tends to get more tired as the day progresses and feels very weak at night. Molecular analysis reveals autoantibodies against the AchR, and you therefore diagnose the patient w/ Myasthenia Gravis. Explain the pathogenesis of this disease and what test MUST be performed next to rule out a further complication of this disease?
Dx: Myasthenia Gravis
Complement activation leads to shedding of the Ach-receptor rich portions of the NMJ along with IgG cross-linking receptor proteins leading to receptor endocytosis. ***The anti-receptor antibodies do NOT directly block binding of Ach to prevent neuromuscular transmission.
This patient should be advised to have a chest x-ray to rule out a thymoma and should also be advised to have a thymectomy since her risk of thymoma is now increased.
A 43 year old male presents with fatigue, muscle wasting, and proximal muscle weakness is all extremities. On a whim you order a chest x-ray and notice several small nodules bilaterally. You diagnose the patient with small cell lung carcinoma. What is the most likely cause of this patient’s presenting symptoms and what is its pathogenesis?
Dx: Lambert-Eaton Syndrome
IgG antibodies target voltage-gated Ca ion channels necessary for Ach release, thus reducing the number of these channels in presynaptic membranes, ultimately reducing the amount of Ach released.
Rx: corticosteroids
A 23 year old female comes to your office and says that she cannot work out anymore w/o pain throughout her body. To investigate this complaint, you have the patient run on the treadmill in your office until fatigue. You then take a urine sample and notice severe myoglobinuria. Muscle biopsy comes back normal, so you send a sample off for a biochemical assay. What is the most likely diagnosis?
Dx: Carnitine Palmitoyltransferase Deficiency
Pt cannot transport long-chain FA into mitochondria
A young infant is brought into your office by 2 very concerned parents stating that the baby just seems very weak. On exam, you notice hypotonia and areflexia. You also notice macroglossia and cardiomegaly. Ultimately, you make the diagnosis of Pompe disease. What would you expect to see on biopsy of this patient’s muscle?
Dx: Pompe disease
Biopsy: Massive accumulation of membrane bound glycogen, inactive satellite cells
Due to Acid Maltase (alpha-1,4-Glucosidase) deficiency. Glycogen is not broken down, accumulates w/in lysosomes and remains membrane bound
A 17 year old male presents with muscle fatigue and weakness, and severe muscle cramping when he engages in strenuous exercise. He is diagnosed w/ McArdle disease. What enzyme is deficient in this patient?
Dx: McArdle Disease
Myophosphorylase deficiency
A 63 year old female presents with diffuse myalgias and an elevated creatine kinase. You make the diagnosis of rhabdomyolysis. The patient states that they recently got over a viral infection, what infection did they most likely have? During the medical history, what drug do you want to see if this patient is taking that could have precipitated their condition?
Dx: Rhabdomyolysis secondary to Influenza
You want to see if the patient is on a statin as they can cause rhabdomyolysis. (alcoholism can be associated w/ rhabdomyolysis also)
A muscle biopsy shows type grouping. What kind of pathology does this patient have?
LMN denervation of muscle
One of your patients suffering from polymyositis is on corticosteroids in an effort to relieve their symptoms. This patient now presents to your office with worsening weakness. Your initial thought is that the patient’s polymyositis has gotten worse. However, what else must you consider? And how might you go about determining the cause of this patient’s decline?
You must consider steroid myopathy. Large doses of steroids can cause muscle weakness w/ type II atrophy. Therefore, this pt’s weakness could be due to a relapse of polymyositis or it could be due to their steroid therapy. To determine the cause, a creatine kinase level should be obtained. Steroid toxicity induced weakness does NOT show an elevation in CK levels and biopsy would show type II atrophy w/o muscle degeneration or inflammation (in contrast to polymyositis).
