Spontaneous Activity of Alpha Motor Neurons in Intramedullary Spinal Cord Tumor

T HIS report describes an instance of alpha rigidity in man, secondary to an infiltrating spinal cord tumor. The usual cases of hypertonicity in man have, in recent years, been attributed solely to an abnormality affecting primarily the stretch reflex as modulated by the gamma efferent system. Landau and Clare, ~,~ and others, have cast experimental doubt on that thesis, but there have been only rare descriptions in the literature of instances of muscular hypertonicity thought to result primarily from hyperexcitability in the alpha motor neuron system. Rushworth, e t a l . , ~1 reported a man with rigidity and constant muscular contractions in the arms, which they attributed to isolation of alpha motor neurons by an infiltrating spinal tumor. Penry, e t a l., 9 reviewed the literature and found six cases of rigidity thought due to alpha motor neuron dysfunction, and added three cases of their own, one of which was the same as that reported by Rushworth, e t al . Subsequently Tarlov ~4 reported two cases of alpha rigidity due to cystic disease of the spinal cord. The above reports comprise 11 cases of rigidity secondary to alpha motor neuron dysfunction. Of these, one case was due to cervical spinal cord tumor, 12 one was associated with necrotizing myelopathy, 9 six resulted from damage to the spinal cord of the newborn, 9 one occurred after cervical trauma, 9 and two occurred with cystic disease of the cord. 15 The case to be described in this report resulted from a tumor in the thoraco-lumbar cord, and the evidence of spontaneous or isolated alpha motor neuron activity was ex-