THE HETEROGENEITY OF MUSCLE BIOPSY FINDINGS OF INFANTS WITH CONGENITAL MYOTONIC DYSTROPHY

Objectives: Profound neonatal hypotonia associated with facial diplegia, poor sucking, dysphagia and respiratory problems are typical findings in patients with congenital myotonic dystrophy (DM(1 and other severe forms of congenital myopathies or dystrophies. This presentation exemplifies some of the diagnostic difficulties in 3 patients with congenital DM1.

Methods: Our investigation included clinical evaluation, muscle biopsy and molecular genetic analysis with DNA probe, which shows CTG trinucleotide expansion at the DM1 gene.

Results: Two patients with DM1 were diagnosed thirteen and eight years ago, shortly after birth, as having myotbular myopthy. The diagnosis was based on clinical picture of severe neonatal hypotonia, facial weakness and feeding difficulties. Serum creatine kinase was normal. Muscle biopsy showed in both patients abundant rows of large central nuclei suggestive of myotubular (centronuclear) myopathy. Years later, with the progress of the clinical picture (which showed clinical improvement in the muscle tone and motor abilities associated with cognitive impairment) and the molecular genetic techniques, we challenged this diagnosis and found that both patients have CTG trinucleotide expansion in the DM gene which is diagnostic for myotonic dystrophy. A muscle biopsy was performed in another patient with a history of severe neonatal hypotonia and feeding difficulties. This biopsy showed non-specific necrosis and macrophagic infiltration of the muscle fibers. At three years of age physical examination showed improvement of the hypotonia associated with facial weakness and cognitive impairment. Molecular analysis of the DM gene demonstrates CTG trinucleotide expansion of the DM gene diagnostic for myotonic dystrophy.

Conclusion: These cases clearly show that in patients with clinical picture suspicious for congenital DM or congenital myopathies muscle biopsy findings may lead to erroneous diagnoses. In such patients DNA probe for the diagnosis of DM should be undertaken before biopsy.