Electromyography in myoadenylate deaminase deficiency (MADD)

Introduction: Myoadenylate deaminase deficiency (MADD) is the most frequent enzyme defect in muscle. However, the frequency of electromyographic changes are not well described. Therefore, the aim of this study was to systematically investigate electromyographic abnormalities in MADD.

Methods: (Altogether) 1673 muscle biopsy samples (1977–1999) were examined for MADD (loss of the AMPD activity). 34 patients (=1,8%, 19 male, 15 female) were diagnosed as MADD and classified as primary symptomatic MADD (n=4), primary asymptomatic MADD (n=8) or coincidental MADD (n=22). Electromyographic of all 34 (20) patients records were retrospectively assessed.

Results: 7 patients showed myopathic, 6 patients neurogenic and 7 patients no abnormalities. In respect to the clinical presentation, myopathic changes were found in 25% of the patients with primary asymptomatic MADD, in 66% within primary symptomatic MADD and in 31% within coincidental MADD. Neurogenic changes were found neither in primary symptomatic nor primary asymptomatic MADD, but in 46% of patients with coincidental MADD. Normal electromyography data showed up in 75% of the patients with primary asymptomatic MADD, in 33% within primary symptomatic MADD and in 23% within coincidental MADD.

Conclusions: 66% of patients with primary symptomatic MADD have myopathic changes despite lack of light or electron-optically recognizable muscular changes. Thus, EMG seems to be a sensitive tool to detect MADD induced abnormalities. But a normal electromyography does not exclude a MADD and a biopsy is recommended if there is clinical suspicion. Neurogenic changes more likely refer to a coincidental MADD but conditions other than MADD need to be considered.