New roentgenologic findings in myotonic dystrophy. An analysis of 18 patients

Human mandibular shape is associated with masticatory muscle force

Understanding how and to what extent forces applied to the mandible by the masticatory muscles influence its form, is of considerable importance from clinical, anthropological and evolutionary perspectives. This study investigates these questions. Head CT scans of 382 adults were utilized to measure masseter and temporalis muscle cross-sectional areas (CSA) as a surrogate for muscle force, and 17 mandibular anthropometric measurements. Sixty-two mandibles of young individuals (20–40 years) whose scans were without artefacts (e.g., due to tooth filling) were segmented and landmarked for geometric morphometric analysis. The association between shape and muscle CSA (controlled for size) was assessed using two-block partial least squares analysis. Correlations were computed between mandibular variables and muscle CSAs (all controlled for size). A significant association was found between mandibular shape and muscle CSAs, i.e. larger CSAs are associated with a wider more trapezoidal ramus, more massive coronoid, more rectangular body and a more curved basal arch. Linear measurements yielded low correlations with muscle CSAs. In conclusion, this study demonstrates an association between mandibular muscle force and mandibular shape, which is not as readily identified from linear measurements. Retrodiction of masticatory muscle force and so of mandibular loading is therefore best based on overall mandibular shape.

A Painless Retroauricular Mass in A Patient with Myotonic Dystrophy: Computed Tomographic Documentation of the Bone Changes that Occur in the Skull Base

A 16-year-old male with a history of neonatal myotonic dystrophy had a painless enlarging left retroauricular mass. Computed tomography showed an enlarged frontal sinus, thickened apparently normal bone in the anterior left clinoid process, doresum sellae, and all portions of the temporal bones. In particular, there was bone production in the left retroauricular region and along the margins of the left internal auditory canal. The left temporomandibular joint was also dislocated. This is the first case report to document the dynamic aspect of the bone changes in this dystrophy.

Masticatory muscle function in patients with spinal muscular atrophy

The purpose of this study was to determine whether spinal muscular atrophy affects masticatory muscle strength and mandibular range of motion. A sample of 15 subjects with spinal muscular atrophy was compared to a sample of age-matched and sex-matched controls. Maximum bite force, masticatory muscle electromyography activity, mandibular ranges of motion and masticatory muscle endurance were evaluated. Results showed that maximum bite forces were one-half as great for the sample with spinal muscular atrophy than for the controls, even though their EMG activity was not significantly different. Slopes of the relationship between electromyography activity and bite force were two to four times steeper for patients with spinal muscular atrophy than controls. Maximum opening and protrusion were reduced to approximately one-half control values. Fatigue times of patients with spinal muscular atrophy were reduced by 30% (17.9 seconds versus 11.1 seconds). We conclude that the masticatory muscles of patients with spinal muscular atrophy are weakened, that their muscles are less efficient, and that they fatigue more quickly than controls. In addition, mandibular movements of these patients take place over a more limited range than unaffected controls.

Craniofacial development in myotonic dystrophy

Anthropometric, cephalometric, and dental data from 23 subjects (12 males and 11 females) afflicted with myotonic dystrophy were compared to similar data from normal subjects who participated in the Iowa Facial Growth Study. A two by two analysis of variance showed that myotonic subjects differed from normal subjects in headlength, head breadth, cephalic index, bizygomatic face width, nosebreadth, maxillary arch widths, palatal depth, anterior and posterior face heights, cranial base lengths, cranial base angles, and other cephalometric measures. Sex differences were observed for many of the variables. It is hoped that these findings will assist clinicians who treat patients having this disorder.

Bone anomalies in myotonic dystrophy

Sixteen patients with myotonic dystrophy underwent CT examination of the skull, and measurement of bone mineral density at lumbar spine and hip by dual-photon absortiometry. The results were compared with those of 20 normal subjects of similar age and sex distribution. Hyperostosis of the calvarium, and increased bone mineral density at lumbar vertebrae were observed. One case showed basal ganglia calcification associated with hyperparathyroidism secondary to deficiency of vitamin D. In the other 15 patients, studies of calcium metabolism were normal. There results suggest the existence of generalized hyperostotic potential in patients with myotonic dystrophy.

Computed tomographic findings of brain and skull in myotonic dystrophy

Twenty-four patients with myotonic dystrophy underwent computed tomographic examination of the skull and brain. The results were compared with those of 20 normal subjects of similar age and sex distribution. Microcephaly and thickening of the calvarium were frequently observed. Some cases showed basal ganglia calcification. Our findings confirm that cranial hyperostosis and brain pathology is a common manifestation of this systemic disease.

Mitral valve prolapse in myotonic dystrophy

Forty-three patients with myotonic dystrophy (MyD) and 43 age- and sex-matched controls were prospectively evaluated for mitral valve prolapse (MVP) using both cardiac auscultation and echocardiography (ECHO). Prevalence of MVP was significantly increased in MyD patients when using either abnormal auscultation plus abnormal ECHO (23.3%, P less than 0.02) or abnormal ECHO alone (30%, P less than 0.01) as diagnostic criteria for MVP. Frequency of MVP was even more increased in patients with a thin, flat chest compared with patients with normal physical appearance (P less than 0.007). These findings are in support of the concept that the increased frequency of MVP in neuromuscular disorders is likely due to geometrical changes of the heart caused by thorax deformities, rather than structural changes of the mitral valve. For this reason, MVP in MyD probably belongs to the entity of so-called benign, secondary MVP. This is further supported by the absence of symptoms of "systemic" complications of MVP in our patient population.

Intestinal absorption in myotonic dystrophy

Forty-four patients with myotonic dystrophy were subjected to various tests for intestinal absorption. A varying number of patients were subjected to the various tests. In one patient (of altogether 11 patients) a pathological vitamin A absorption test was found together with increased faecal excretion of fat and nitrogen. Two of 12 patients showed pathological D-xylose tests. The reason for this may possibly be deficient urine collection. Schilling tests were on the whole normal. Glucose tolerance tests were pathological in 26 of 35 patients. The following pathological findings were made: elevated fasting blood sugar, elevated peak level, delayed return to pretest level, biphasic response and reduced increment in blood glucose levels following loading. The biphasic response seems to be a rather characteristic finding in myotonic dystrophy. The peak concentration was in all except one case reached within 15-60 minutes. Intravenous glucose loading gave normal response curves. The pathological response on oral loading was probably often caused by intestinal motility disturbances and not by malabsorption. Malabsorption seems to be a rare feature of myotonic dystrophy.