Laterality of bolus passage through the pharynx in patients with unilateral medullary infarction

Laterality of bolus passage in the pharynx is often seen in patients with medullary infarction. We evaluated the dominant side of bolus passage in the pharynx and investigated the factors that cause the passage to dominantly occur on the affected side. Forty-one patients (35 men and 6 women, 64 ± 9 years) with unilateral medullary infarction participated in this study. Bolus passage of 4 mL of thick liquid was evaluated in 3 regions (oropharyngeal, thyropharyngeal, and cricopharyngeal) and classified into 4 patterns (dominantly on the unaffected side [UAS], on both sides without clear laterality [BS], dominantly on the affected side [AS], and nonpassage of the bolus [NP]) by videofluoroscopic examination of swallowing. The bolus passages were as follows: UAS, BS, and AS occurred in 2, 32, and 7 patients in the oropharyngeal region; UAS, BS, and AS occurred in 5, 20, and 16 patients in the thyropharyngeal region; and UAS, BS, AS, and NP occurred in 11, 9, 10, and 11 patients in the cricopharyngeal region, respectively. In the thyropharyngeal region, the proportion of patients in whom the swallowing reflex occurred when the bolus was in the oropharynx and the proportion of patients with unilateral pharyngeal constrictor paralysis were greater in patients whose bolus passage was AS than in patients whose passage was BS. This suggests that the bolus predominantly passed through the affected side of the thyropharyngeal portion because of the asymmetry of pharyngeal contraction during swallowing in the early period after onset.