The short exercise test is normal in proximal myotonic myopathy.
OBJECTIVE
Proximal myotonic myopathy (PROMM) is a multisystem disorder that may mimic myotonic dystrophy (MD). Previously we demonstrated that the 60 s exercise test was normal in two siblings with PROMM. The test enabled distinction of PROMM from MD, as there is a well documented immediate post-exercise compound muscle action potential (CMAP) amplitude decline in MD.


METHODS
We now performed exercise testing using several exercise durations in 8 PROMM patients from 6 kinships, and one MD patient, extending our previous observations. Repetitive stimulation and needle electromyography findings were also recorded.


RESULTS
The 10 (n = 8), 30 (n = 5), and 60 (n = 5) s, and the 5 min (n = 1) exercise tests were normal in all PROMM patients. Specifically, the maximum post-exercise CMAP amplitude decline was 8%. In contrast, the MD patient had CMAP amplitude declines of 48% (10 s exercise test) and 26% (30 s exercise test). The distribution of repetitive stimulation and motor unit duration abnormalities were variable and less diagnostically useful.


CONCLUSIONS
The 10, 30, and 60 s exercise tests help distinguish PROMM from MD. As the 10 s exercise test is rapid and easily tolerated, we recommend this test for clinical testing.
Sander
H W
HW
Department of Neurology, Saint Vincents Hospital of New York, NY 10011, USA. hsander@saintvincentsnyc.org
Scelsa
S N
SN
Conigliari
M F
MF
Chokroverty
S
S
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D000368:Aged; D004558:Electric Stimulation; D004576:Electromyography; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009132:Muscles / Q000503:physiopathology; D009223:Myotonic Dystrophy / Q000503:physiopathology*