Reduced cerebral blood flow and impaired visual–spatial function in proximal myotonic myopathy

Objective: To compare brain involvement in myotonic dystrophy (DM) with that of proximal myotonic myopathy (PROMM). Background: PROMM is a multisystem disease with many features in common with DM. Methods: Twenty patients with DM (CTG [500–700] ), 20 patients with PROMM, and 20 normal control subjects were studied. Neuropsychological testing was performed in 12 patients with PROMM and in 18 patients with DM; brain MRI was performed in 17 of 20 PROMM patients and 15 of 20 DM patients. Ten patients with PROMM and 11 patients with DM were subjected to H 2 15 O PET. Results: Two-thirds of the patients with PROMM and one-half of those with DM were impaired on visual–spatial recall, whereas one-third of the patients with PROMM and less than half of those with DM showed an impairment in visual–spatial construction. Brain MRI was normal, or showed only nonspecific white matter abnormalities in both PROMM and DM patients. PET studies in PROMM patients showed a bilateral decrease in regional cerebral blood flow (rCBF) of the orbitofrontal and medial frontal cortex, whereas DM patients had more widespread hypoperfusion that extended to the dorsolateral frontal cortex and subcortical regions. Conclusions: Impaired visual–spatial function may be present in proximal myotonic myopathy. This correlates best with a reduction in regional cerebral blood flow observed in H 2 15 O PET brain scans rather than with specific structural abnormalities observed on brain MRI.