There are many factors that can cause your puppy to shake his legs. The most common reason for this behavior is an overactive thyroid gland (hyperthyroidism). This condition, however, only accounts for about 1% of cases in dogs. Other causes include: Chronic kidney disease Infection Hypothyroidism Sudden changes in diet Excessive exercise Pregnancy Cushing’s disease Intestinal blockage Painful urination Stress Dietary deficiencies Kidney failure Heartworm infection Drugs Inflammatory bowel disease Spinal cord injury Anxiety Paralysis