My sweet Maltese Shih tzu is 17 months old. The vet has checked her thorougly more than once and cannot find the cause but my dog will suddenly chew her left wrist as if she's being bitten. But no signs of anything. She has monthly Advantage to prevent fleas, no ticks in our area and she's well groomed. This is not boredom as she will wake up from a sound sleep and attack like she's extremely itchy. She does like to roll around or lay in the small sand in the driveway but she's brushed well each evening before bed. Anyone have a similar experience or an idea. She's on a special diet due to crystals in her urine. A trait of her breed.