A 54-year-old man comes to the office due to seeing double while watching TV at night. The sensation resolves when he closes either eye. The patient gets a mild headache when he experiences double vision but has no associated nausea, vomiting, photophobia, or phonophobia. According to his wife, his voice gets a little "nasal" in the evening. He has no other medical problems and does not use tobacco, alcohol, or illicit drugs.
The patient's vital signs are normal. His eyes are shown in the image below. Eye movements are full, and pupils are equal and equally reactive to light with a brisk response. Funduscopic examination is normal. There is no extremity weakness or sensory loss. He is stable in the Romberg position. The remainder of the physical examination is normal.

Which of the following is the best next step in management of this patient?

Question

A 54-year-old man comes to the office due to seeing double while watching TV at night.  The sensation resolves when he closes either eye.  The patient gets a mild headache when he experiences double vision but has no associated nausea, vomiting, photophobia, or phonophobia.  According to his wife, his voice gets a little "nasal" in the evening.  He has no other medical problems and does not use tobacco, alcohol, or illicit drugs.
The patient's vital signs are normal.  His eyes are shown in the image below.  Eye movements are full, and pupils are equal and equally reactive to light with a brisk response.  Funduscopic examination is normal.  There is no extremity weakness or sensory loss.  He is stable in the Romberg position.  The remainder of the physical examination is normal.

Which of the following is the best next step in management of this patient?

Quizplus · Accepted Answer

11ec193a_987f_7450_853d_0f2513b8cd32_MD0002_00 This patient's double vision that presents at night and resolves when he covers either eye is suggestive of fatigable diplopia; the nocturnal nasal quality of speech indicates palatal muscle weakness. This fluctuating and fatigable weakness is most suggestive of myasthenia gravis (MG), an autoimmune disorder of the postsynaptic neuromuscular junction that can affect ocular, bulbar, limb, and/or respiratory muscles. It may present as ocular myasthenia (disease limited to extraocular muscles and eyelids) or generalized disease. Ocular muscle weakness is the most common presenting symptom of MG, and ptosis may be unilateral or bilateral or switch eyes over time. In this patient, spared pupillary response helps distinguish MG from Horner syndrome, and involvement of the extraocular muscles (oculomotor, trochlear, and abducens nerves [CNs III, IV, and VI]) and palate (glossopharyngeal and vagus nerves [CNs IX and X]) helps distinguish MG from Bell palsy (facial nerve [CN VII]). Diagnosis is confirmed with serologic testing. More than 85% of patients with generalized MG are positive for acetylcholine receptor (AchR) autoantibodies, which are highly specific for MG. However, only 50% of patients with ocular MG are positive for AchR antibodies. Approximately 40% of patients who are seronegative for AchR antibodies are seropositive for muscle-specific tyrosine-kinase (MuSK) autoantibodies. If serologies are completely negative, electromyography and a nerve conduction study with repetitive nerve stimulation are indicated to confirm the diagnosis before aggressive treatment is initiated. The edrophonium and ice pack tests are no longer recommended as first-line testing due to high false-positive results (Choice C). If serologic tests or nerve conduction studies are positive, MG treatment can be started. Pyridostigmine (acetylcholinesterase inhibitor), the first-line treatment, is generally well tolerated. Corticosteroids are usually indicated for acute crisis and for those unresponsive to initial therapy (Choices D and E). MG treatment TSH should be checked in all patients due to MG's high association with autoimmune thyroid abnormality. In patients with high suspicion of other autoimmune disorders, testing (eg, antinuclear antibody panel) is indicated as appropriate. Because 15% of patients have a thymoma, CT scan or MRI of the chest should be performed once the MG diagnosis is confirmed (Choice B). Educational objective: Diagnosis of myasthenia gravis consists of serologies (anti-acetylcholine receptor and anti-muscle-specific kinase antibodies) and nerve conduction studies in a stepwise manner. Pyridostigmine (acetylcholinesterase inhibitor) is the first-line treatment. TSH and CT scan or MRI of the chest (to look for a thymoma) should be ordered in all patients diagnosed with this condition. __________ References: Muscle autoantibodies in myasthenia gravis: beyond diagnosis? (http://www.ncbi.nlm.nih.gov/pubmed/22882218) The difficulty in confirming clinical diagnosis of myasthenia gravis in a seronegative patient: a possible neurophysiological approach. (http://www.ncbi.nlm.nih.gov/pubmed/19846306)

A 54-Year-Old Man Comes to the Office Due to Seeing