A positive babinski sign, which is the 1st movement of the toe being upwards in stimulation of the sole of the foot, has a broad range of causes. I cannot tell you what the diagnosis is based on the information you provide. It could be cervical spondylosis and this is very common in the elderly. It is always abnormal, but whether it is just a age-related degenerative spine or a stroke I do not know. An MRI of the head and neck is a good way to go.
Good luck
Hello.
While it is true that Babinski reflex is an abnormal finding, it can also be relatively nonspecific. In fact, a good neurologist can elicit a babinski reflex in just about anyone. Having said that, however, your father may, in fact, have several reasons for the Babinski reflex to be present. Some prior-alcohol related changes in the brain can lead to the presence of all of the above findings. B12 deficiency is certainly a reasonable assumption. However, in the absence of any "focal" findings, a stroke or a tumor should not be high on the list.
I would, however, make sure that your dad has an MRI of the neck before any sort of a PET scan, as in the presence of neck pain, it may explain both weakness in the legs and a Babinski reflex. Cervical spondylosis is one of the most common findings in older people and should be taken seriously.
Good luck!
ON