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

Objective: To compare brain involvement in myotonic dystrophy (DM) with tha t of proximal myotonic myopathy (PROMM). Background: PROMM is a multisystem disease with many features in common with DM. Methods: Twenty patients wit h DM (CTG([500-700])), 20 patients with PROMM, and 20 normal control subjec ts were studied. Neuropsychological testing was performed in 12 patients wi th PROMM and in 18 patients with DM; brain MRI was performed in 17 of 20 PR OMM patients and 15 of 20 DM patients. Ten patients with PROMM and 11 patie nts with DM were subjected to (H2O)-O-15 PET. Results: Two-thirds of the pa tients with PROMM and one-half of those with DM were impaired on visual-spa tial recall, whereas one-third of the patients with PROMM and less than hal f of those with DM showed an impairment in visual-spatial construction. Bra in MRI was normal, or showed only nonspecific white matter abnormalities in both PROMM and DM patients. PET studies in PROMM patients showed a bilater al decrease in regional cerebral blood flow (rCBF) of the orbitofrontal and medial frontal cortex, whereas Dill patients had more widespread hypoperfu sion that extended to the dorsolateral frontal cortex and subcortical regio ns. Conclusions: Impaired visual-spatial function may be present in proxima l myotonic myopathy. This correlates best with a reduction in regional cere bral blood flow observed in (H2O)-O-15 PET brain scans rather than with spe cific structural abnormalities observed on brain MRI.