Myotonic Dystrophy type 2 (DM2) often has variable manifestations with varying degrees of proximal weakness, grip myotonia, and nonspecific symptoms such as muscle pain and stiffness that can result in significant diagnostic challenges. Unlike its counterpart type 1, the multisystemic aspects and physical manifestations of the disease process are much less apparent. This often results in a delay in diagnosis with consequent increased morbidity and mortality. 

We present three patients who had mild symptoms of proximal muscle weakness in the limbs, with their exam showing subtle proximal weakness. Grip and percussion myotonia was absent or minimally noted. However, strikingly, they all shared evidence of profound neck flexor weakness that was best elicited mainly when examined in the supine position and was easily missed, when tested in the sitting position.

All of our patients underwent electrodiagnostic studies. The EMG displayed evidence of prominent myotonic discharges in multiple muscle groups, which in the context of their phenotype indicated the likely diagnosis of DM2 and led us to order the CCTG expansion genetic testing, for which all 3 patients tested positive.

In today's age, genetic studies have become widely available at low cost and rapid turnaround.  Often times, neurologists may bypass electrodiagnostic studies in the setting of similar history. However, the abnormal CCTG repeats in the 3q21 zinc finger protein 9 (ZNF9/CNBP) gene are not detected on next-generation sequencing myopathy panels.  

In this era of advancing technology, these cases underscore the importance of a thorough neuromuscular examination, in combination with electrodiagnostic studies that can lead to targeted specific gene testing.