These monsters are actually humans in the last stage of Cabin Fever, a disease caused by prolonged confinement. They look like hairy, bestial humanoids. They are inevitably naked, since the sufferer cannot abide the feeling of clothing on their skin and will tear it from their body. They are extremely violent, and hysterical in behaviour, screaming and repeating words they hear without any sense.
Cabin Fever often occurs in arctic environments, where a hunter might be 'snowed in' and have to stay in one place for weeks. The Piblokto appears to be uneffected by the cold. Yet they will eventually die, apparently of exposure, if they are not cured.
The cure, difficult or impossible though it may be, is to take the sufferer to a warm place, with people around, not to restrain them but to ignore their behaviour, only defending oneself when necessary. until after several weeks they will return to sanity and change back to human form.