Here we have the distinction between demon possession and illness.
The Healings Of Jesus
When Jesus healed a man with leprosy there was nothing to indicate He thought the man was demon-possessed.
Immediately the leprosy left him, and he was made clean . . . [Jesus] said to him, “See that you say nothing to anyone; but go, show yourself to the priest, and offer for your cleansing what Moses commanded, as a testimony to them” (Mark 1:42,44).
There were many cases of people whom Jesus healed in which there was no mention of demon possession. These included people who were mute, blind, and deaf. In none of these cases do we find the writers of Scripture attributing their illness to the demonic.
One of the passages that seems to link sickness and demon possession is found in Mark.
And they brought the boy to Him. When the spirit saw Him, immediately it convulsed the boy, and he fell on the ground and rolled about, foaming at the mouth. Jesus asked the father, “How long has this been happening to him?” And he said, “From childhood. It has often cast him into the fire and into the water, to destroy him; but if You are able to do anything, have pity on us and help us” (Mark 9:20-22).
This boy, who had symptoms of epilepsy, was actually possessed by a demon. Scripture makes the distinction between the two.
And the news about Him went out into all Syria; and they brought to Him all who were ill, taken with various diseases and pains, demoniacs, epileptics, paralytics; and He healed them (Matthew 4:24).
More Than Usual Symptoms
Those who were demon-possessed had physical manifestations of their possession. This included such things as: seizure, speech impediments, muteness, deafness, and blindness. The manifestations of these afflictions were beyond the normal symptoms for the particular ailment. There was something unusual about their symptoms that caused them to be attributed to demons. Yet others, who had the same affliction, were not assumed to be demon-possessed, but rather merely sick. Scripture is careful to make the distinction between the two.
The Bible says that disease and demon-possession are not to be equated. Scripture makes the clear distinction between sickness and demon-possession. There are example of people who are demon-possessed that have physical afflictions. However others with the same afflictions are not considered to be demon-possessed. It is wrong therefore, to equate certain kinds of illness to demon-possession.