Pruritic Urticarial Papules 瘙痒性丘疹荨麻疹
Case Report
A 11-year-old boy, with no medical history, was presented with round erythematous pruritic lesions (approximately 0.5 to 2 cm in diameter) which were localised on his back (Figure by iPhone Xs Max Day 1). His history revealed that the eruption had developed suddenly 12 hours ago, after an evening forest trail while viewing monkeys at MacRitchie Reservoir. The patient stated that he had never experienced a similar reaction to mosquito or any kind of insect bite before. On examination, his overall health condition was good. There was no dermographism. Mucous membranes and joints were not involved, and there was no peripheral oedema. The patient was treated with systemic antihistamines (cetirizine and chlorpheniramine) and anticeptic moisturizing cream.
The normal reaction to an insect bite is an inflammatory reaction at the site of the punctured skin, which appears within minutes and consists of pruritic local erythema and edema. The symptoms usually subside within a few hours. Local reactions are caused by irritant substances concentrated in insect saliva (anticoagulants, enzymes, agglutinins, and mucopolysaccharides). A local reaction is followed by delayed skin reactions consisting of local swelling, itching, and redness that resolve after systemic antihisamines. However a second urticarial eruption spreaded the next day on the chest and back (Fig. Day 2). Patient complained about the severe itch and burning sensation. Antihistamine did not help. Herbal systemic medicaiton was initiated immediately two times daily, the rash raised areas continuned enlarging and merging together on Day 3 and 4, pruritic urticarial papules faded on day 5, itching was reduced gradually. One week after herbal systemic therapy, the urticarial papules from the first eruption resolved without any sequelae.
Discussion
“Urticaria” is the medical term for hives. Hives are raised areas of the skin that itch intensely and are red with a pale center. Hives are a very common condition. About 20 percent of people have hives at some time during their lives.
Hives develop when there is a reaction that activates immune cells in the skin called mast cells. When activated, these cells release natural chemicals. One important chemical involved is histamine, which causes itching, redness, and swelling of the skin in an area: a hive. In most cases, hives appear suddenly and disappear within several hours.
In some cases, eg. we reported above, the raised areas enlarge and merge together, refractory to antihistamines therapy. Papular urticaria is usually presented with clusters of itchy red bumps (papules) without systemic symptoms. Itching is severe enough to interfere with the patient’s study and sleep. Papular Urticaria is thought to be an immunological reaction to insect bites, it most often occurs in children. This is because desensitisation to insect bites has not yet developed. It is also called a persistent insect bite reaction.
Fleas and mites that live on cats and dogs are most often responsible to papular urticaria. Not everyone with papular urticaria has pets, and it can sometimes be difficult to work out what a patient is reacting to. There have been reports of reactions to mosquitoes, gnats, bird mites, carpet beetles, caterpillars, flea, lice and other insects. Papular urticaria is normally self-limiting, but exceptions always exist. The immunological basis of this reaction means that it may take months or even years for children to become desensitised to the causal insect.
全家去森林徒步麦理芝蓄水池看猴子后的第二天，小弟的背后出了一些红丘疹。以为蚊虫叮咬，或者接触到了过敏原，擦了止痒药膏吃了抗组胺药，应该很快会好转起来。不料第二天，丘疹接连成片，又红又厚又痒，布满前胸后背，抗组胺药(cetirizine and chlorpheniramine) 完全无效，皮疹演化成瘙痒性丘疹性荨麻疹。丘疹性荨麻疹被认为是对昆虫叮咬的免疫反应，它最常发生在儿童中。这是因为儿童对昆虫叮咬的脱敏尚未发展。它也被称为持续性昆虫叮咬反应。马上自家中药口服每日两次；第三天，荨麻疹持续扩大非常痒，已经不能进行户外活动，光着膀子躲在房间；第四天，荨麻疹面积继续扩大，但是已经开始由厚变薄，第五天后皮疹开始脱落；第六天正常新皮涌现，痒减轻。经过一周的口服中药治疗，丘疹性荨麻疹完全消退。
生活在猫和狗身上的跳蚤和螨虫最常导致丘疹性荨麻疹，然而并非每个患有丘疹性荨麻疹的人都有宠物，有时候很难弄清楚患者到底对什么反应。有报道称蚊子、蚂蚁、鸟螨、地毯甲虫、毛毛虫、跳蚤、虱子和其他昆虫均可导致此反应，可能是由昆虫唾液中浓缩的刺激性物质（抗凝剂、酶、凝集素和粘多糖）引起。丘疹性荨麻疹通常是自限性的，但例外永远存在。这种反应的免疫学基础意味着儿童可能需要数月甚至数年的时间才能对此昆虫脱敏。
