Evidence for central abnormality in respiratory control in primary lateral sclerosis.

Primary lateral sclerosis (PLS) is a very rare disease characterized by pure upper motor neuron findings. Although a number of previous reports have evaluated this condition, no study has addressed the respiratory function in PLS. Six patients meeting previously proposed diagnostic criteria for PLS were submitted to a number of respiratory tests: forced vital capacity, maximal pressures, phrenic nerve responses, needle electromyography of the respiratory muscles, percutaneous nocturnal oximetry (PNO) and polysomnography (two patients). Our results show that the diaphragm is not affected in this condition, but some respiratory function tests (RFT) and PNO had abnormal values. Voluntary muscular activation to perform RFT may be limited in these patients. PNO and polysomnography suggest that respiratory central drive dysfunction can occur when upper motor neurons are severely affected, in PLS. However, we did not verify progression on follow-up.