Case 2 Clinical History and Physical Exam: This 34 year old woman first noted in
ID: 3484158 • Letter: C
Question
Case 2
Clinical History and Physical Exam: This 34 year old woman first noted intermittent horizontal diplopia and droopiness of her eyelids in her early twenties. It was worse when she was tired and it slowly progressed to the point that the diplopia became constant by age 30. The following year, she developed weakness in her legs with frequent falls and difficulty climbing stairs. She noted muscle pain if she walked for a prolonged time. She denied having fatigability in her limb muscles.
Cranial nerve testing revealed an almost complete external opthalmoplegia with only a few degrees of movement in all directions. There was also bilateral eyelid ptosis and fatigability. Motor examination showed normal tone and bulk. There was mild proximal weakness in the upper and lower extremities with fatigability after repetitive movement. Reflexes were diminished. The rest of the neurological exam was normal.
Laboratory Findings: A tensilon test showed a positive response with improvement of at least 50% of her eyelid ptosis.
Electrodiagnostic studies done to rule out a neuromuscular junction disorder (repetitive nerve conductions and single fiber EMG) were normal. Acetylcholine receptor antibodies were not detected. The serum CK was normal.
Microscopic Analysis: Sections of muscle tissue revealed mild variation in fiber size. Some of the fibers had the features of ragged red fibers with disruption of the intermyofibrillar network and abnormal subsarcolemmal accumulations of granular refractile material which may represent mitochondria. Several fibers had internally placed nuclei. Inflammatory infiltrates were absent.
Case 2 Question 1: The symptom of diplopia is related to the _____ muscles, specifically, the horizontal movement is attributable to the _____ and _____ rectus muscles.
Case 2 Question 2: What is “ptosis?”
Case 2 Question 3: The negative result for acetylcholine receptor antibodies rules out _____ _____ as a diagnosis. (Note: Yes, the internet will tell you that there are exceptions to this, but in most cases it is correct.)
Case 2 Question 4: The microscopy finding of "ragged red fibers" means that there is a defect in which organelle in the muscle cells?
Explanation / Answer
Answer 1) related to the extra ocular muscles. The horizontal movement is attributed to the lateral and medial rectus muscle.
Answer 2) the drooping of the upper eyelid is known as ptosis.
Answer 3) myasthenia gravis. Myasthenia gravis (MG) can cause weakness of the eyelids and extra ocular muscles in up to 90% of patients.
Answer 4) mitochondria. When muscle is stained with Gomori Trichrome, characteristic ragged-red fibers are visible under the microscope. This appearance is due to the accumulation of abnormal mitochondria below the plasma membrane of the muscle fiber.
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