Idiopathic Inflammatory Myopathy with Delayed Finger Opening Resembling Grip Myotonia

• Published in: Internal Medicine Vol. 62; no. 22; pp. 3397 - 3400
• Main Authors: Kobayashi, Shunsuke, Shimizu, Jun, Hatanaka, Yuki, Kanbayashi, Takamichi, Sonoo, Masahiro
• Format: Journal Article
• Language: English
• Published: Japan The Japanese Society of Internal Medicine 15.11.2023; Japan Science and Technology Agency
• Subjects: Case Report; delayed finger opening; extensor digitorum; Finger; idiopathic inflammatory myopathy; Inflammation; Internal medicine; Myopathy; Myotonia; myotonic dystrophy; idiopathic inflammatory myopathy; myotonic dystrophy; delayed finger opening; myotonia; extensor digitorum
• ISSN: 0918-2918; 1349-7235; 1349-7235
• DOI: 10.2169/internalmedicine.1545-22

Grip myotonia can be a clue for the diagnosis of myotonic disorders. However, several clinical conditions cause delayed finger opening mimicking grip myotonia. We herein report a 44-year-old man with idiopathic inflammatory myopathy who presented with delayed finger opening resembling grip myotonia. The delayed finger opening differed from grip myotonia given the absence of the warm-up phenomenon and percussion myotonia, relative sparing of the thumb extension, and pronounced weakness of the extensor digitorum. Focusing on the extension of the thumb and other fingers may aid in the differentiation between delayed finger opening and true grip myotonia.