Diagnosis of Lafora disease by skin biopsy.

The Lafora type of progressive myoclonus epilepsy is a rare and fatal familial disease characterized by seizures, myoclonus, and dementia. This diagnosis was confirmed in 2 patients by demonstrating the presence of intracytoplasmic polyglucosan bodies, or Lafora bodies, in the peripheral portion of the eccrine sweat gland duct. Exclusive use of the periodic acid-Schiff stain is recommended for demonstrating these diagnostic inclusions. Electron microscopy reveals fine pale-staining filaments, fine dark-staining granules, and dark-rimmed vacuoles within these non-membrane-bound inclusions. Skin biopsy is the preferred method of confirming the diagnosis of Lafora disease.