A 65-year-old man is being evaluated for new-onset ptosis. Earlier in the day, the patient underwent right total knee arthroplasty for advanced osteoarthritis with no operative complications. While in the postoperative recovery unit, he had difficulty opening his left eye and developed slurred speech. The patient has never had these symptoms, and his preoperative neurologic examination was unremarkable. He has no prior history of double vision, difficulty swallowing, or limb weakness. Medical history includes ischemic stroke with no residual deficits, type 2 diabetes mellitus, hypertension, and a 20-pack-year smoking history. Temperature is 36.7 C (98.1 F), blood pressure is 150/90 mm Hg, pulse is 92/min, and respirations are 12/min. Neurologic examination reveals bilateral ptosis, left greater than right. Pupils are equal in size and reactive to light. An ice pack is placed over the closed eyelids for 2 minutes, leading to improvement of the ptosis. Which of the following is the most likely cause of this patient's current symptoms?

Question

A 65-year-old man is being evaluated for new-onset ptosis.  Earlier in the day, the patient underwent right total knee arthroplasty for advanced osteoarthritis with no operative complications.  While in the postoperative recovery unit, he had difficulty opening his left eye and developed slurred speech.  The patient has never had these symptoms, and his preoperative neurologic examination was unremarkable.  He has no prior history of double vision, difficulty swallowing, or limb weakness.  Medical history includes ischemic stroke with no residual deficits, type 2 diabetes mellitus, hypertension, and a 20-pack-year smoking history.  Temperature is 36.7 C (98.1 F), blood pressure is 150/90 mm Hg, pulse is 92/min, and respirations are 12/min.  Neurologic examination reveals bilateral ptosis, left greater than right.  Pupils are equal in size and reactive to light.  An ice pack is placed over the closed eyelids for 2 minutes, leading to improvement of the ptosis.  Which of the following is the most likely cause of this patient's current symptoms?

Quizplus · Accepted Answer

11ec25c8_d489_7d8d_bc81_cf1d5d44d6c4_MD0003_00 This patient's symptoms are concerning for myasthenia gravis (MG), a neuromuscular disorder caused by autoantibody-mediated degradation of acetylcholine receptors at the neuromuscular junction. MG usually presents in the sixth to eighth decade in men and the second and third decade in women with fluctuating fatigable weakness involving the extraocular (eg, ptosis, diplopia) and bulbar (eg, dysphagia, dysarthria) muscles. Weakness can be exacerbated by various factors, including medications (eg, aminoglycosides, magnesium, beta blockers, neuromuscular blocking agents), surgery (particularly thymectomy), pregnancy, or infections. This patient was likely exposed to a neuromuscular blocking agent (eg, rocuronium) during intubation, which unmasked his symptoms. ptosis The diagnosis of MG can be supported with the bedside ice pack test, in which an ice pack is applied over the eyelids for several minutes, leading to an improvement in ptosis. The cold temperature improves muscle strength by inhibiting the breakdown of acetylcholine at the neuromuscular junction, thereby increasing acetylcholine availability to the nicotinic receptor. Patients with positive test results should undergo confirmatory testing for MG with acetylcholine receptor antibodies (highly specific). (Choice B) Disruption of the oculosympathetic chain causes Horner syndrome, which is characterized by ipsilateral ptosis, miosis, and anhidrosis. (Choice C) Lambert-Eaton myasthenic syndrome, a paraneoplastic disorder associated with small cell lung cancer, is caused by autoantibodies directed against presynaptic calcium channels in the neuromuscular junction, which leads to impaired acetylcholine release. Patients typically have slowly progressive proximal muscle weakness and depressed deep tendon reflexes. Although ocular manifestations (eg, diplopia, ptosis) may occur, they are not usually the presenting symptoms and would not improve in response to the ice pack test. (Choice D) Bell palsy is characterized by inflammation and edema of the facial nerve (often due to herpes simplex activation) and typically presents with sudden-onset unilateral facial paralysis. (Choices E and F) Oculomotor nerve palsy (mydriasis, ptosis, and down-and-out deviation of the eye) may occur with nerve compression (eg, due to a posterior communicating artery aneurysm or an uncal herniation) or microvascular nerve ischemia (eg, due to diabetes mellitus). Nerve compression is more likely to cause mydriasis, as parasympathetic fibers are situated on the periphery of the oculomotor nerve. Educational objective: The diagnosis of myasthenia gravis can be supported with the bedside ice pack test. In this test, an ice pack is applied over the eyelids for several minutes, leading to an improvement in ptosis. Patients with positive test results should undergo confirmatory testing for acetylcholine receptor antibodies (highly specific). References: The use of the ice pack test in myasthenia gravis. (http://www.ncbi.nlm.nih.gov/pubmed/21103106) The place of the ice pack test in the diagnosis of myasthenia gravis. (http://www.ncbi.nlm.nih.gov/pubmed/15529523) Ice pack test for myasthenia gravis. (http://www.ncbi.nlm.nih.gov/pubmed/3614664)

A 65-Year-Old Man Is Being Evaluated for New-Onset Ptosis