MOTOR-NEURON DISEASE - A PRIMARY DISORDER OF CORTICOMOTONEURONS

It has been suggested that the primary site of damage in motor neuron disease (MND) is the cortical motor neuron, with secondary degeneratio n of spinal motor neurons. To test this hypothesis, we sought to deter mine if loss of corticomotoneurons in MND precedes spinal motor neuron loss, The density of corticomotoneurons was measured in 18 MND and 9 control cases using 10-mu m horizontal sections of motor cortex in the hand/arm region. The density of spinal motor neurons was measured in 10-mu m transverse sections of the lower cervical spinal cord, Cortico motoneuron and spinal motor neuron densities were decreased in MND cas es compared to controls, but in MND cases there was poor correlation ( r(2) = 0.06) between corticomotoneuron and spinal motor neuron densiti es, The results indicate that corticomotoneuron and spinal motor neuro ns are lost at different rates in different MND patients, and that cor ticomotoneuron loss is unlikely to be a primary event in MND. (C) 1995 John Wiley & Sons, Inc.