Causes of thin tail in leopard gecko?

Your leopard gecko could be skinny due to malnutrition. Offer your animal some live feeders gutloaded and coated in calcium. If you notice your leo's tail starts to become wavy, these are the first signs of MBD (metabolic bone disease). Meaning the animal is now drawing calcium from its bones in order to survive due to the lack in diet. Once MBD has taken place It will start to draw calcium from the limbs, head and spine. At this point the disease is not reversible.