Difficulty Standing on the Tiptoes? Think of an Epiconus Syndrome: A Case Report and a Review of the Pathobiology of the Conus and Epiconus

Abstract

The motor deficits, urogenital dysfunction and perineal numbness of the conus medullaris syndrome are well known. Less well known is the disease of the epiconus, the spinal cord immediately above the conus medullaris. The disease is quite unique with ankle plantar-flexion weakness that usually exceeds ankle dorsi-flexion weakness. The epiconus syndrome can present with both upper and lower motor neuron findings and manifest unique findings on nerve conduction/electromyography studies. Intriguingly, lumbo-sacral corticospinal tract disease can involve trans-synaptic degeneration of the anterior horn motor neurons and lead to acute denervation, as recorded with electromyography. The conus medullaris also contains Onuf's nucleus, which controls penile erection, ejaculation, the external urethral and the external anal sphincter and is the basis of the bulbo-cavernosus reflex. Extension of a lesion from the epiconus to the conus can lead to urogenital dysfunction. We seize upon a case of an epiconus syndrome in order to outline some of these fascinating observations including the pathobiology of the conus and epiconus. In order to understand the epiconus, one must be versed with the conus medullaris.