Scleroderma
Also referred to as progressive systemic sclerosis, it is a very rare autoimmune disease. The disease is not well understood, scientists seem to think it occurs when your immune system provokes the overproduction of a fibrous protein called collagen that results in thickened and hardened skin.
Scleroderma is a very chronic disease and requires immediate treatment to slow down its progression. It can result in swelling and damage to various organ systems, tissues, and joints. It could also be the cause of your sudden pain and stiffness in your ankle.
Achilles tendonitis
This is when there is an injury with your Achilles tendon, a part of your body that connects your heel to your calf muscle. It can also be a result of overstressing your Achilles tendon, leading to wear and tear. Aging can also be a factor, the older you grow the weaker your tendons are. This condition makes it difficult to move or flex your foot.