Abstract
Background: The purpose of this study was to evaluate the electrophysiological characteristics of Hirayama disease.
Method: Electrophysiological characteristics were analyzed retrospectively in 50 patient diagnosed of Hirayama disease by clinical, imaging and electrophysiological studies. Electrophysiological studies include electromyography (EMG) and nerve conduction studies (NCS).
Results: Among 50 patients, 49 were male. The mean age (mean ± s.d.) of the patients was 19.98 ± 2.83 years. In NCS, abnormal amplitude of compound muscle action potential (CMAP) < 5 mv were found in Ulnar nerve in 76% of patients and Median nerve in 24% of cases. The mean amplitude for ulnar and median nerve was 3.5 ± 2.64 mv and 9.1 ± 3.97 mv. The Ulnar/Median (U/M) compound muscle action potential (CMAP) amplitude ratio is found to be ≤0.6 in 80% of patients. Distal latencies and F-wave latencies were variably affected. Conduction velocities were normal in all nerves. Sensory conduction study was absolutely normal in all the patients. Neurogenic changes were found in bilateral hand muscles in 96% of patients.
Conclusions: Though asymmetric pattern is the predominant clinical presentation, needle EMG found neurogenic changes in most of the patients. In Hirayama disease, thenar muscles of hand are preferentially involved than hypothenar muscles, a reverse Split Hand pattern. Ulnar to median nerve compound muscle action potential (CMAP) ratio are useful methods in arriving at the correct diagnosis of Hirayama disease and should be an essential part of the protocol to differentiate from other motor neuron diseases as Hirayama disease is self limiting and early diagnosis can limit disability in young adults.
Keywords: Hirayama disease, Electrophysiological study, reverse split hand.
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Corresponding Author
Krittika Palchoudhury
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DOI: https://dx.doi.org/10.18535/jmscr/v6i4.78
