Upper motor neuron involvement in Kennedy disease evaluated by triple stimulation technique

Abstract

To explore the presence of subclinical upper motor neuron (UMN) dysfunction in Kennedy disease (KD) patients with triple stimulation technique (TST). At our hospital from July 2013 to July 2014, a total of 20 KD patients with clinical manifestations, genetic testing and routine electrophysiological tests were examined by triple stimulation technique (TST) combining transcranial magnetic stimulation (TMS) of motor cortex with peripheral collision studies. And the results were expressed by TST amplitude ratio (TST test/TST control). All patients had typical presentations and were genetically proved. The expansion size of polymorphic tandem cytosine-adenine-guanine (CAG) repeat in the first exon of androgen receptor gene was (44 ± 5). Electromyography showed acute and chronic neurogenic damage. Sensory nerve action potentials declined in amplitude. TST amplitude ratio was normal for 13 KD patients and 7 cases were significantly altered. Tendon hyperreflexia was found in 1 patient with normal TST. In patients with abnormal TST, central motor conduction time (CMCT) was normal in 4 patients and tendon hyperreflexia was found in 5 patients. The possible reasons for 7 patients with abnormal TST were concurrent lacunar infaction (n = 2), concurrent spondylotic myelopathy (n = 2) and KD alone (n = 3). Subclinical involvement of UMN may be present in KD patients while other potential causes must be excluded.