[Centronuclear myopathy: clinical characteristics and MRI image features of oral and maxillofacial region]

Objective: To provide biomechnical basis for orthodontics of centronuclear myopathy (CNM) patients, we studied the oral and maxillofacial clinical features and MRI image manifestations to explore application of MRI to objective evaluation the affected facial muscles. Methods: The study consisted of 8 patients who were diagnosed as CNM (CNM group) and 20 healthy volunteers (control group). Their medical information were gathered and then we examined the ptosis situation and the facial index calculation of them. To measure the maximal hight of palate and the width of palate, patients and volunteers were made impressions. We also checked their maximum bite force with occlusion pressure tester. And they took lateral cephalometric radiographs to measure mandibular plane-Frankfort horizontal plane angle (MP-FH). At last, they were taken oral and maxillofacial region MRI to observe the affected situation of masseter muscle, medial pterygoid muscle and lateral pterygoid muscle. Results: Six patients were ptosis; 6 patients had inverse V-shaped mouth; 3 patients were difficulty in swallowing; 4 patients were anterior open bites; 4 patients were mouth breathing; 7 patients liked to eat soft foods. Morphological facial index ([91.3±0.5]%), MP-FH (34.9°±2.0°) of CNM group were greater than the control group, male maximal hight of palate ([19.0±0.2] mm), female maximal hight of palate ([18.0±0.6] mm) of CNM group were greater than the control group (P<0.05). Male width of palate ([34.5±0.8] mm), female width of palate ([33.4±1.0] mm), male maximum bite force ([464.3±78.2] N), female maximum bite force ([320.7±13.8] N), maximal opening of mouth ([3.4±0.3] cm) of CNM group were less than the control group (P<0.05). And these had significant difference compared with the control group (P<0.05). In MRI examination, there were 7 patients' masseter muscles, 4 patients' medial pterygoid muscles and 6 patients' lateral pterygoid muscles to atrophy asymmetrically. These three pieces of muscular fatty infiltration were inordinately, focused on Grade 0 to 4 and the both sides were similar. Conclusions: CNM patients with long and thin face, high palatine arches and low bite force together were the biomechanical basis of the maxillofacial deformities. MRI can clearly show the affected masseter muscle, medial pterygoid muscle, lateral pterygoid muscle, and can serve as an objective examination method for the evaluation of facial muscles. It can be worth of clinical popularization and application.