Slowly Progressive Ophthalmoplegia as a Presenting Symptom of Myotonic Dystrophy Type 1.

M yotonic dystrophy Type 1 (DM1) is an autosomal dominant disorder caused by expansion of cytosine– thymine–guanine (CTG) triplet repeats within the dystrophia myotonica protein kinase (DMPK) gene on chromosome 19 (1). Because DM1 affects both skeletal and smooth muscles, patients with DM1 manifest various symptoms, including ocular, cardiac, gastrointestinal tract, and endocrine system impacts. Cataract and myotonia are common presenting symptoms, and patients with small expansion of CTG triplet repeats (mild DM1) may show only these symptoms and have a normal lifespan (1). External ophthalmoplegia is rarely reported as an early sign of DM1 relative to limb weakness. In this article, we report a patient with DM1 who manifested chronic progressive ophthalmoplegia as a presenting symptom. A 51-year-old man presented with progressive painless ophthalmoplegia and bilateral ptosis lasting more than 2 years. The ocular symptoms did not fluctuate and had progressed slowly. His history was unremarkable, except cataract surgery in both eyes 8 months previous. He denied any family history of neurological disorders. On neurologic examination, the patient’s face demonstrated atrophy of the temporalis muscles (Fig. 1). He also showed bilateral incomplete ptosis (i.e., interpalpebral fissure measured 6/6 mm) and exotropia in the left eye in the primary position. The right and left pupils were anisocoric (3 and 4 mm, respectively), with an oval irregular shape of the left one. The pupils were reactive during the light reflex assessment but slightly sluggish. He demonstrated limitations of adduction and supraduction of the left eye and a limitation of supraduction of the right eye (Fig. 2). He showed saccadic pursuit and saccades were hypometric with relatively normal velocity within the limited range of motion. The other cranial nerves were unremarkable. Although he complained of subjective weakness of his hands, an examination revealed no weakness. Meanwhile, the deep tendon reflexes were hypoactive, and there was no handgrip myotonia or percussion myotonia of the limb and trunk muscles. However, mild percussion myotonia of the tongue was observed. Laboratory tests revealed that the serum concentrations of free T4, thyroid-stimulating hormone, antithyroid antibodies, and antiacetylcholine receptor antibodies were within normal limits. Brain MRI findings were normal, and electromyography showed typical myotonic discharges in the right proximal and distal limb muscles and masseter. Genetic testing for DM1 confirmed the presence of a greater-than-150 CTG triplet expansion in the DMPK gene. Our patient with progressive bilateral ptosis and ophthalmoplegia was eventually diagnosed with DM1. His “hatchet face” and history of cataracts were clues that led to our suspicion of DM1, despite the absence of a family history. Several reports have described neuroophthalmologic manifestations of DM1. In such instances, the pupil becomes miotic, and the light reflex turns sluggish as the disease progresses (2). Another report revealed that saccades were usually slow, but the latency and accuracy of saccades did not change significantly, and the smooth pursuit gain was normal in DM1. The maximum velocity of saccades was shown to be correlated with limb muscle