Decreased muscular radionuclide uptake in Tc-99m MIBI scintigraphy during paralytic phase of thyrotoxic periodic paralysis.

The underlying pathophysiology of thyrotoxic periodic paralysis (TPP) is still obscure. From histologic surveys, vacuole formation and abundant mitochondrial abnormalities ranged from swelling, matrical pallor, pleomorphism, and reduced cristae were often disclosed in the muscle fibers during paralytic periods. In a 47-year-old man experiencing 2 episodes of transient paralysis, hyperthyroidism with TPP was diagnosed. During the acute paralytic phase, a significant reduction of radionucleotide uptake in the quadriceps on Tc-99m sestamibi scintigraphy was found, aside from the previous morphologic findings, that it further suggests impaired mitochondrial integrity and cellular viability in TPP.