<unk>  is persistent blue or cyanotic discoloration of the extremities, most commonly occurring in the hands, although it also occurs in the feet and distal parts of face. Although described over 100 years ago and not uncommon in practice, the nature of this phenomenon is still uncertain. The very term<unk> " is often applied inappropriately in cases when blue discoloration of the hands, feet, or parts of the face is noted. The principal (primary) form of<unk>  is that of a benign cosmetic condition, sometimes caused by a relatively benign neurohormonal disorder. Regardless of its cause, the benign form typically does not require medical treatment. A medical emergency would ensue if the extremities experience prolonged periods of exposure to the cold, particularly in children and patients with poor general health. However, frostbite differs from<unk>  because pain (via thermal nociceptors) often accompanies the former condition, while the latter is very rarely associated with pain. There are also a number of other conditions that affect hands, feet, and parts of the face with associated skin color changes that need to be differentiated from<unk> : Raynaud phenomenon, pernio, acrorygosis, erythromelalgia, and blue finger syndrome. The diagnosis may be challenging in some cases, especially when these syndromes co-exist.<unk>  may be a sign of a more serious medical problem, such as connective tissue diseases and diseases associated with central cyanosis. Other causative conditions include infections, toxicities, antiphospholipid syndrome, cryoglobulinemia, neoplasms. In these cases, the observed cutaneous changes are known as "secondary<unk> ". They may have a less symmetric distribution and may be associated with pain and tissue loss.
Acrocyanosis
Nail clubbing
Cyanosis
Maculopathy
Rhagades
Retinopathy
Hyperthecosis
Pathergy