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Itchy skin disease

Pruritus key points test

Regarding itch: #! Itch is the sensation that results in scratching # Itch is transmitted via A-fibres from free nerve endings in the skin # Medial spinothalamic tract lesions disrupt itch #! Neuropathic itch is often dermatomal Explanation: Itch is defined as the sensation that that results in scratching. It is transmitted via specific C-fibres from free nerve endings in the skin, and passes via the lateral spinothalamic tract. Neuropathic pruritus may be dermatomal but is localized and non-dermatomal or widespread. Itch can be induced by: #! Histamine # Opioid antagonists #! Substance P #! Serotonin Explanation: Mediators of pruritus include mechanical and electrical stimuli and chemicals including histamine and substance P. Itch can be induced by centrally acting serotonin and opioids. Itch is most often due to the following skin diseases: #! Dermatitis # Skin cancer #! Urticaria #! Infestation Explanation: Dermatitis affects about 20% of the population at one time or other and is nearly always intensely itchy. Urticaria affects one third of the population. Although often very itchy, most episodes are acute and have cleared up within a few days. Scabies and lice infestations result in intense pruritus. Skin cancer is usually asymptomatic although characteristically squamous cell carcinoma is tender. Itch may be due to the following systemic diseases: #! Polycythaemia rubra vera #! Primary biliary cirrhosis #! Chronic renal failure #! Hodgkin’s disease Explanation: Itch may be due to various systemic diseases including all those listed. Treatment of itch may include: # Topical tretinoin #! Moisturisers #! Sedation # Warm environment Explanation: Itch remains hard to suppress in some patients but cooling the skin, applying moisturizers, relaxation and sedation, oral antihistamines and antidepressants may be helpful.