Last month an older ferret that was having problems with his rear legs came in to the veterinary clinic. In older ferrets weakness in the rear legs is common, and it can be caused by many different things. The two most common diseases that cause rear-leg weakness are insulinoma and lymphoma.
Insulinoma is a cancer of the pancreas. This cancer produces excessive insulin. Too much insulin causes the blood-sugar level to decrease. When the blood sugar becomes low, the ferret becomes weak and wobbly in the rear legs. In worst-case situations, the blood sugar can become low enough to cause seizure activity.
Lymphoma is a cancer of the lymphocytes that can involve most organs and lymph nodes. This cancer can also affect the brain and spinal cord. Damage to the spinal cord can cause weakness in the rear legs.
The physical exam did not reveal any enlarged lymph nodes, organs, or damage to the spinal cord or nerves in the legs. The blood-glucose level was then checked, and it was in the normal range. Thus the ferret did not have an insulinoma causing the problem. It was also unlikely that he had lymphoma based on his high activity level, good appetite and normal physical exam.
Now it was time to look for the unusual problems. After watching the little guy walk around, it was clear that he was only having a problem with one of his legs. The ferret had no history of trauma or anything odd happening to him. Careful palpation of the leg did not reveal any swollen areas or painful spots. Thus it was unlikely he had a broken bone in his little leg. More palpation revealed a problem with his knee. He had a cranial drawer sign in his knee, which means he had torn his anterior cruciate ligament (ACL) just like a football player.
This is an uncommon injury in ferrets, but it can happen as a ferret comes down a ramp in its cage. If the rear paw gets stuck in the ramp while the ferret is going downhill, it can tear the ligament in the knee. Fortunately this is a treatable condition. Surgery can be done to repair the knee, or cage rest can be used to allow scar tissue to help stabilize the knee.