Abstract
A 47-year-old woman with dysphagia and ptosis gradually developed dysarthria and muscular weakness. Magnetic resonance imaging, testing for anti–acetylcholine receptor antibodies, edrophonium chloride (EC) test, and electrophysiologic test revealed no abnormalities. A psychogenic reaction was suspected. Four months after disease onset, the patient presented to our hospital. In videofluoroscopic examination of swallowing (VF), there was no aspiration for swallowing of either liquid or soft food. It revealed, however, poor pharyngeal constriction, no epiglottis inversion, repeated swallowing movements, and large amounts of pharyngeal residue. Videofluoroscopic examination of swallowing after an intravenous injection of 10 mg EC showed improvements in all above observations; particularly, it was clear when swallowing soft food. Furthermore, the anti–muscle-specific kinase (MuSK) antibody titer was elevated, and anti-MuSK antibody–positive myasthenia gravis (MuSK-MG) was diagnosed. Thus VF during EC test may be helpful in diagnosing MuSK-MG in patients with dysphagia.
1
Introduction
Myasthenia gravis (MG) that is positive for anti–muscle-specific kinase (MuSK) (MuSK-MG) accounts for only 27% to 38% of anti–acetylcholine receptor (AChR) antibody–negative MG. Muscle-specific kinase MG is associated with bulbar symptoms, such as dysphagia and dysarthria, from an early stage ; therefore, these patients often present with the chief complaint of difficulty in swallowing. They need to consult an otolaryngologist before a definite diagnosis of MuSK-MG is made because MuSK antibody titer is measured in only some laboratories. The edrophonium chloride (EC) test, which evaluates the improvement of muscle weakness after intravenous EC injection, is positive in only 65.6% of patients with MuSK-MG in contrast to 88.6% of patients with anti–AChR antibody–positive MG (AChR-MG) .
Videofluoroscopic examination of swallowing (VF) before and after intravenous EC injection is useful for the evaluation of dysphagia during the course of AChR-MG ; however, whether it contributes to the diagnosis of MuSK-MG is unknown. This is the first case report that describes changes in swallowing movements before and after EC injection in a patient with MusK-MG.
2
Case report
A 47-year-old woman with dysphagia, dysarthria, ptosis, and general muscular weakness gradually developed difficulty in speaking and bilateral ptosis 1 month after the onset of difficulty in swallowing. Her medical, lifestyle, and family history were unremarkable.
The findings for cranial magnetic resonance imaging (MRI), neck MRI, and laboratory investigations were normal. The EC test was negative, and the cause of her symptoms remained undiagnosed. At 2 months after symptom onset, the patient experienced choking while drinking water, could raise both arms only to the shoulder level, and had to hold on to railings when climbing stairs. After 3 months, she developed drooping of the neck (muscle weakness). The repetitive nerve stimulation test gave normal results, and the anti-AChR antibody test was negative; therefore, a psychogenic reaction was suspected. After 4 months, she presented to our hospital for the evaluation of dysphagia.
Blood pressure was 108/76 mm Hg, and the pulse was 86 per minute and regular. There was no respiratory distress, and the SpO 2 was 99%. Consciousness was intact. The patient complained of difficulty in chewing and swallowing food. Bilateral ptosis was observed. Hypernasality was noted with poor bilateral soft palate elevation. Facial muscle strength was decreased, and cheek puffing could not be maintained. Tongue protrusion was in the midline, and there was no atrophy or muscular fasciculation of the tongue. The gag reflex was intact. The proximal muscle groups were weaker than the distal muscle groups, with no left-right difference. No diurnal variations in muscle strength were observed. Tendon reflexes were decreased, and no pathologic reflexes were noted. Autonomic nervous symptoms, sensory disturbances, and cerebellar ataxia were not noted. Laboratory investigations, including thyroid function and creatine kinase levels, were normal. Respiratory functions and electrocardiogram were also normal.
We performed all x-ray fluoroscopic examinations after obtaining the patient’s written informed consent, and the x-ray fluoroscopy time was less than 5 minutes. We evaluated the swallowing motion using 10 mL of 2-fold diluted 110% wt/vol barium solution (liquid) and 8 g of barium corned beef (soft food). The same evaluation was repeated after intravenous injection of 10 mg EC. All swallowing motions were recorded on DVD at 30 frames per second, and after the test, 1 examiner analyzed all VF clips using PC software Move-tr/2D 7.0 (Library Inc., Tokyo, Japan) and Adobe Photoshop CS5 (Adobe Systems Ins., San Jose, CA, USA).
The pharyngeal area before the start of swallowing (PA hold) was 13.4 cm 2 . On VF before EC injection, the liquid in the oral cavity could not be retained by the tongue and soft palate. Pharyngeal constriction during swallowing was poor, and the maximum pharyngeal constriction (PA max) was 5.1 cm 2 with a pharyngeal constriction ratio (PCR) of 0.38 (normal, 0.03 ± 0.03) . The soft palate did not elevate, and the epiglottis did not invert ( Fig , A). Liquid reflux into the mouth was noted. There was no aspiration for either liquid or soft food swallowing. After swallowing, both the liquid and the soft food remained in the epiglottic vallecula and piriform sinus. In particular, soft food residues remained at the base of the tongue and posterior hypopharyngeal wall ( Fig , B). The pharyngeal transit duration (PTD) for the soft food was 8.06 seconds. The number of swallows for the liquid was 8, whereas that for the soft food was 10.
On VF after EC injection, oral retention of the liquid was possible, and pharyngeal constriction improved. The PA max was 3.2 cm 2 , and the PCR was 0.23. The soft palate did not elevate, but the epiglottis did invert ( Fig , C). The PTD of the soft food improved to 6.15 seconds. There was no aspiration of the liquid or the soft food. The number of swallows decreased to 4 for the liquid and soft food each, and pharyngeal residues also decreased ( Fig , D; Table ). The patient was aware of the improvement in swallowing function after EC injection while consuming the soft food.
| Measurement parameter | Before EC injection | After EC injection | |
|---|---|---|---|
| With liquid | PCR | 0.38 | 0.23 |
| No. of swallows | 8 | 4 | |
| Soft palate elevation | None | None | |
| Epiglottis inversion | None | Present | |
| Pharyngeal residues | – | – | |
| With soft food | No. of swallows | 10 | 4 |
| PTD (s) | 8.06 | 6.15 | |
| Pharyngeal residues | – | – |
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