Greyscale, a highly contagious disease that hardens the skin, causing it to look grey and hard as stone. It initially spreads on the victims skin, but with the time passing it destroys the inside of the body as well. The disease also causes a change in the victims behavior, leading to a sort of terminal madness. It is one of the most deadly diseases on Westeros. The transmission of the disease is said to occur even though a simple touch by an infected person or by an object an infected person has touched.
Given the background of the Grayscale and its main characteristics, it is highly possible that the Greyscale is a strange mix of a couple of real diseases we have on Earth.
Leprosy is a chronic bacterial infection caused by the Mycobacterium leprae, named from the Greek word for scales “lepra”. The disease itself is contagious and with time it spreads throughout the body causing granulomas of the nerves, the skin, the respiratory tract and the eyes. This results in a lack of ability to feel pain and the loss of body parts. There are two types of the disease, which diverse in the severity of the disease itself, one being mild and with few lesions (sores on the skin) and only slightly contagious, and the other being severe, widespread on the body and more contagious.
Ichthyosis is a heterogeneous family of at least 28 skin disorders, which are mostly genetic. Even though this disease is not a infectious one and can not be transmitted, its signs and symptoms are very similar to the Greyscale. The disease is characterized by dry, rough, thickened, scaly and flaky skin which is said to resemble the scales on a fish, from what derives the name of the disease itself (in Ancient Greek ichthys means fish). The disease is progressive and with time destroys all the skin, causing pain and agony.
Calcinosis is a term used to describe a group of disorders of the skin with a different background in which calcium deposits form in the skin, making it look scaly, with ulcerated plaques and hard subcutaneous nodules.
FOP (Fibrodysplasia ossificans progressiva), sometimes referred to as Stone Man Syndrome is a rare disease of the connective tissue, cause by a genetic mutation of the body’s repair mechanism, causing fibrous tissue (muscle, tendon and ligament) to ossify spontaneously when injured. The late stages of the disease are characterized by the affection of the internal organs causing a slow and painful death.
Rabies is a viral disease that causes acute inflammation of the brain in humans and other warm-blooded animals. Although the disease itself is incurable and kills in a short period of time, it resembles the final stages of the Greyscale because of its affection of the behavior, with an progressive insanity and a tedious death.