Thanks for your question on Healthcare Magic. I can understand your concern. PML is progressive multiple leukoencephalopathy. It is progressive disease of brain. Hyperventilation at night in these patients is suggestive of respiratory center involvement. This is also suggestive of worsening disease. These kind of patients also show day time hyperventilation and ultimately succumb to death. BiPAP device is useful for respiratory problems. Hope I have solved your query. I will be happy to help you further. Wishing good health to your patient. Thanks.