Relative sparing of extraocular muscles in myotonic dystrophy: an electrooculographic study

External Ophthalmoplegia and Brainstem White Matter Lesions: Presentation of Myotonic Dystrophy Type 1

INTRODUCTION

Myotonic dystrophy type 1 (DM1) is an autosomal dominant condition which phenotype can be extremely variable considering its multisystem involvement, including the central nervous system. Neuromuscular findings are facial and distal extremities muscle weakness, muscle atrophy and myotonia. Standard diagnosis is obtained with molecular testing to detect CTG expansions in the myotonic dystrophy protein of the kinase gene. Brain magnetic resonance imaging typically shows characteristic subcortical white matter (WM) abnormalities located within anterior temporal lobes.

CASE REPORT

We present a 39-year-old male patient with a progressive external ophthalmoplegia, facial and limb muscle weakness, percussion myotonia and atypical brain magnetic resonance imaging findings, showing confluent brainstem WM lesions, affecting the pons, a rare radiologic feature in this disorder. Genetic testing confirmed the diagnosis for DM1.

CONCLUSION

This presentation with external ophthalmoplegia and brainstem WM loss in DM1 can show an important correlation with clinical findings and have an important diagnostic and prognostic value.

Bilateral Adduction Palsy in a Patient with Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is caused by CTG repeat expansion in the DMPK gene in chromosome 19q13.3. External ophthalmoplegia is a rare manifestation in DM1. We report a DM1 patient confirmed by the presence of 650 CTG triplet expansions in the DMPK gene and had limitation of adduction gaze bilaterally. Brain MRI showed bilateral medial rectus muscles atrophy. Our patient provides additional evidence of ocular motor muscle involvement in DM1.

Sparing of the extraocular muscles in mdx mice with absent or reduced utrophin expression: A life span analysis

Sparing of the extraocular muscles in muscular dystrophy is controversial. To address the potential role of utrophin in this sparing, mdx:utrophin(+/-) and mdx:utrophin(-/-) mice were examined for changes in myofiber size, central nucleation, and Pax7-positive and MyoD-positive cell density at intervals over their life span. Known to be spared in the mdx mouse, and contrary to previous reports, the extraocular muscles from both the mdx:utrophin(+/-) and mdx:utrophin(-/-) mice were also morphologically spared. In the mdx:utrophin(+/)(-) mice, which have a normal life span compared to the mdx:utrophin(-/-) mice, the myofibers were larger at 3 and 12 months than the wild type age-matched eye muscles. While there was a significant increase in central nucleation in the extraocular muscles from all mdx:utrophin(+/)(-) mice, the levels were still very low compared to age-matched limb skeletal muscles. Pax7- and MyoD-positive myogenic precursor cell populations were retained and were similar to age-matched wild type controls. These results support the hypothesis that utrophin is not involved in extraocular muscle sparing in these genotypes. In addition, it appears that these muscles retain the myogenic precursors that would allow them to maintain their regenerative capacity and normal morphology over a lifetime even in these more severe models of muscular dystrophy.

Ocular motor function in relation to gross motor function in congenital and childhood myotonic dystrophy type 1

PURPOSE

To assess ocular motor function in congenital and childhood myotonic dystrophy type 1 (DM1) and correlate the results with cytosine-thymine-guanine (CTG) repeat size, severity of the disease, myotonia and skeletal muscle function.

METHODS

A cross-sectional investigation into strabismus, versions/ductions, saccades, smooth pursuit movements and ptosis was performed on 49 individuals with a confirmed diagnosis of DM1, all diagnosed at <18 years of age and with >40 CTG expansion repeats. The results were correlated with myotonia as well as Hammersmith motor ability scale (HMA). In addition, the ocular results were compared to results from an age and- sex-matched control group.

RESULTS

Ocular motor abnormalities were seen in 82%; the most frequent findings were altered conjugate eye movements and 'pseudoptosis' while blepharoptosis was rare. Strabismus was most common in the severe congenital subgroup, with a frequency 14 times higher than in the control group. Positive correlations were seen between CTG repeat size and affected eyelids, and between myotonia and affected eyelids; both these findings were most prominent in the mild congenital group. CTG repeat size was also correlated with version/duction defects, and most obviously in the childhood group. Low HMA scores were associated with high occurrence of strabismus and version/duction defects.

CONCLUSION

Abnormalities of ocular motor function are frequently present. CTG repeat size correlates positively with altered versions/ductions and eyelid pathology. Gross motor dysfunction correlates with strabismus and defect versions/ductions, and eyelid pathology indicates involvement of myotonia.

Ophthalmoplegia as the presenting muscle-related manifestation of myotonic dystrophy

INTRODUCTION

Myotonic dystrophy type 1 (DM1) is a genetic disorder caused by expanded CTG repeats within the 3' untranslated region of the dystrophia myotonia protein kinase (DMPK) gene on chromosome 19. Diplopia is rare in this disease and has only been reported in patients with diffuse neuromuscular disorders.

OBSERVATION

We report here on the case of a 58-year-old woman in whom ophthalmoplegia was the first neuromuscular manifestation of DM1 and led to the diagnosis. Among the multisystem abnormalities associated with DM1, muscle-related symptoms are prominent, and usually involve the facial and neck muscles early on in the disease. This case provides additional evidence of oculomotor muscle involvement in DM1.

CONCLUSION

DM1 should, therefore, be considered during the diagnostic workup of any unexplained ophthalmoplegia of muscle origin, especially if there has been a previous history of cataract, even in the absence of typical muscle-related features.

Eye movement disorders in myotonic dystrophy type 1

CONCLUSIONS

No definite sign was found of central oculomotor system disorders being independent of saccadic slowing because (1) diminished maximum slow phase velocity of the optokinetic nystagmus (OKNspv) was closely related to saccadic slowing (p<0.01, r=0.59), (2) maximum frequency of optokinetic nystagmus (OKNfq) was normal, (3) visual suppression (VS) change was mild, and (4) the diminished maximum slow phase velocity of the caloric nystagmus (CNspv) seen in some patients is explained by both peripheral and central vestibular involvement. These findings support the extraocular muscle hypothesis.

OBJECTIVE

To assess whether eye movement disorders seen in patients with myotonic dystrophy type 1 (DM1) are caused by central oculomotor system involvement or extraocular muscle damage.

PATIENTS AND METHODS

Oculomotor functions and their correlation with (CTG)n length were studied in 29 DM1 patients and 12 age-matched controls.

RESULTS

Values for saccadic velocity (p<0.005), maximum OKNspv (p<0.005), and maximum CNspv (p<0.01) in the patient group were markedly lower than in the control group. VS of caloric nystagmus in the patient group was slightly lower than that in the controls. No significant difference was found between the two groups in the maximum OKNfq. Patients with greater (CTG)n lengths had lower saccadic velocities (p<0.01, r=0.71).

Eye muscle sparing by the muscular dystrophies: lessons to be learned?

The devastating consequences of the various muscular dystrophies are even more obvious when a muscle or muscle group is spared. The study of the exceptional cell or tissue responses may prove to be of considerable value in the analysis of disease mechanisms. The small muscles responsible for eye movements, the extraocular muscles, have functional and morphological characteristics that set them aside from other skeletal muscles. Notably, these muscles are clinically unaffected in Duchenne/Becker, limb-girdle, and congenital muscular dystrophies, pathologies due to a broken mechanical or signaling linkage between the cytoskeleton and the extracellular matrix. Uncovering the strategies used by the extraocular muscles to "naturally" protect themselves in these diseases should contribute to knowledge of both pathogenesis and treatment. We propose that careful investigation of the cellular determinants of extraocular muscle-specific properties may provide insights into how these muscles avoid or adapt to the cascade of events leading to myofiber degeneration in the muscular dystrophies.

Eye movement abnormalities in myotonic dystrophy

We studied saccade and smooth pursuit eye movements in 31 patients suffering from myotonic dystrophy (MD). On the basis of mean value comparisons, saccades were slower and hypometric and smooth pursuit eye movements performed worse in MD patients than in controls. On an individual basis, saccade duration was prolonged in 67.7%, saccades were hypometric in 19.4%, saccade latency was delayed in 9.7%, and the smooth pursuit performance index was decreased in 9.7% of patients. Eye movement abnormalities did not correlate with those detectable by visual, brain-stem auditory and somatosensory evoked potentials. We attempted to classify eye movement abnormalities as myogenic or neurogenic on the basis of differences in combination of eye movement abnormalities and the occurrence of D5/D35 dissociation; the latter consists of a prolonged duration for large (35 degrees) but not for small (5 degrees) saccades. Since D5/D35 dissociation occurred in 26/33 multiple sclerosis patients with increased saccade duration, we considered it to be a neurogenic pattern attributable to a central nervous system (CNS) dysfunction. A prolonged duration without dissociation especially in combination with saccade hypometria, is interpreted as a myogenic pattern, although the lack of dissociation may also occur with CNS impairment in case of a marked increase in saccade duration. Accordingly we classified the oculomotor abnormalities detected as neurogenic in 11 MD patients and as myogenic in another 10, but in some subjects belonging to the second group concomitant CNS impairment is not to be excluded.