Most PU patients are children; they typically present with multiple, clustered papules, which measure up to one, rarely two centimeters in diameter, and pruritus. In some cases, papules may turn into vesicles. PU is a chronic disorder characterized by spontaneous remission and spontaneous recurrence of skin lesions and in the course of several days or even weeks, papules emerge, merge, subside and emerge again. Adjacent skin regions may show variable degrees of erythema and edema.

While the above described lesions are often localized on exposed skin regions, e.g., face, neck, hands, arms and calves, they may also be observed anywhere else. It cannot be ruled out that papules develop at a certain distance of insect or arachnid bites and thus, distribution of lesions does not necessarily serve as a clue as to where and when patients were exposed to these parasites. Some time may have passed since the patient sustained arthropod bites and the lack of a close temporal connection further complicates recognition of a causal relation.

Skin lesions resolve upon application of topical antihistamines and corticosteroids, but recurrence is to be expected. Symptoms generally resolve in winter, but patients often return during warm summer months of the following year.

Of note, intense pruritus generally has patients scratching the affected areas of the skin and in some cases, deeper skin lesions, hemorrhages and eschar may dominate the clinical picture. Secondary bacterial infection is not uncommon and may lead to pyoderma.

• Pain

  Ibrahim Farag, Dermatologist at Online Dermatology Courses Follow Published on Jun 22, 2015 Insects Bites & Stings: can be divided into 2 groups venomous insect such as a bee or wasp, which uses this as a defense mechanism by injecting toxic and painful [slideshare.net]

  The complication of papular urticaria may include hypopigmentation / hyperpigmentation or depressed or raised scars due to excoriations as a result of painful erosions mostly in darkly pigmented person. [medicalrealm.net]

  691 209 Pseudoxanthoma elasticum 695 210 Psoriasis 697 211 Psychogenic excoriation 708 212 Pyoderma gangrenosum 711 213 Pyogenic granuloma 716 214 Radiation dermatitis 719 215 Raynaud disease and phenomenon 722 216 Reactive arthritis 726 217 Regional pain [books.google.es]

  Some pain-relieving products may also create a sensation such as warmth, cooling, or slight burning to distract someone from itchiness. Most of these products are available over the counter. [thehealthy.com]

• Malaise

  Systemic symptoms like fever, malaise, etc may also be present. If not treated promptly, the condition can be associated with high risk of septicemia. [simple-remedies.com]

  Constitutional symptoms : fever, headache, malaise and soreness of the mouth and throat. The syndrome may present with severe manifestations such as rapid pulse,weakness,rapid respiration, prostration and joint pains. The syndrome may be fatal. [drmhijazy.com]

• Constitutional Symptom

  Mild constitutional symptoms such as fever,malais,myalgia and arthralgia may precede the appearance of the eruption.The disease is self-limiting. Fig.224f. Erythema nodosum (Erythema nodosum was discussed in the previous chapters). [drmhijazy.com]

• Episodic Course

  Of the cases identified until today, two‐thirds have had a chronic course and the remaining a recurrent and episodic course. Recognizing IGD is quite important in order to indicate the underlying autoimmune disorders [ 5, 40 ]. [intechopen.com]

• Urticaria

  In San Francisco, children with papular urticaria due to flea bites are part of dermatologic practice year round. [ncbi.nlm.nih.gov]

  Papular urticaria. Cutis 2001; 68: 89-91. [africanskindiseases.org]

• Insect Bite

  We conclude that a more appropriate term for future study and diagnosis of this entity is insect bite-induced hypersensitivity. [ncbi.nlm.nih.gov]

  The aetiology and progression of reactions to insect bites are now better defined but understanding of the histopathology is relatively poor, mainly because patients have widely differing experiences of exposure to biting insects. [onlinelibrary.wiley.com]

  Also called lichen urticatus, strophulus. pap·u·lar ur·ti·ca·ri·a ( pap'yū-lăr ŭr'ti-kar'ē-ă ) A sensitivity reaction to insect bites, especially human and pet fleas, seen mostly in young children as wheals followed by papules on exposed areas. [medical-dictionary.thefreedictionary.com]

  Alerts and Notices Synopsis   Papular urticaria is a chronic or recurrent pruritic eruption believed to be an allergic (hypersensitivity) reaction to insect bites. [visualdx.com]

  […] be secondary bacterial infection papular urticaria may occur as a complication of any insect bite(s) Links: causes bee stings and wasp stings management skin infections flea bites [gpnotebook.co.uk]

• Papule

  Most PU patients are children; they typically present with multiple, clustered papules, which measure up to one, rarely two centimeters in diameter, and pruritus. In some cases, papules may turn into vesicles. [symptoma.com]

  Overview Papular urticaria is a common and incessantly disturbing disorder manifested by persistent or recurrent papules caused by a hypersensitivity reaction to the bites of mosquitoes, fleas, bedbugs, and different bugs. person papules may encompass [allergyandimmunology.blogspot.com]

  Clusters of red papules surrounded by an urticarial flare due to cat fleas. Papular urticaria. Characteristic red papule with central puncta. Papular urticaria. Giant red flare following insect exposure. Venomous spider bite. [clinicalgate.com]

  Also called lichen urticatus, strophulus. pap·u·lar ur·ti·ca·ri·a ( pap'yū-lăr ŭr'ti-kar'ē-ă ) A sensitivity reaction to insect bites, especially human and pet fleas, seen mostly in young children as wheals followed by papules on exposed areas. [medical-dictionary.thefreedictionary.com]

  Cutis. 2001 August;68(2):89-91 Papular urticaria is a common and often distressing childhood disorder manifested by chronic or recurrent papules caused by a hypersensitivity reaction to the bites of mosquitoes, fleas, bedbugs, and other insects. [mdedge.com]

• Dermatitis

  Atopic dermatitis although clinically described in 1935 has an elusive pathophysiology. The atopic trinity is characterized by barrier dysfunction, allergy, and pruritus. The role of dendritic cells has been studied extensively in atopic dermatitis. [ijpd.in]

  Codes ICD10CM: L50.8 – Other urticaria SNOMEDCT: 55608001 – Papular urticaria Look For Subscription Required Diagnostic Pearls Subscription Required Differential Diagnosis & Pitfalls Insect bites Impetigo Contact dermatitis Exanthematous drug eruption [visualdx.com]

  The prevalences of atopic disease, recurrent wheezing, and atopic dermatitis were higher in the group under 5 years old with papular urticaria than in the same-age control group (p = 0.001, 0.002, and 0.001, respectively). [ibecs.isciii.es]

  Removal of the wood led to resolution of the dermatitis. [medicaljournals.se]

  Keywords Dermanyssus gallinae ; dermatitis ; pruritus ; SEM ; Upper Egypt Statistics Article View: 67 PDF Download: 105 [puj.journals.ekb.eg]

• Blister

  Case 2. 5-year-old boy with blistering episodes only in late spring. [ejpd.com]

  These blisters and bumps can vanish and reappear on the skin. Once a blister vanishes, it oftentimes leaves a darkened mark on the skin. Papular urticaria generally manifests as reddened, itchy bumps or blisters on the skin. [firstaidwinnipeg.ca]

  The bumps and blisters can disappear and reappear on the skin. After a blister disappears, it sometimes leaves behind a dark mark on the skin. Symptoms usually appear in the late spring and summer. [healthline.com]

  In some cases, they may be associated with fluid filled blisters. Repeated scratching of these blisters can lead to secondary infections. These secondary infections often convert the fluid filled blisters into pus filled blisters. [simple-remedies.com]

PU is usually diagnosed during summer months and in geographical regions marked by warm and humid climates during that time of the year. Patients may not associate skin alterations with insect or arachnid bites, because papules often develop at a certain distance to the initial lesion. Also, one single bite may be sufficient to trigger PU and patients may not even consider it worth mentioning. However, they may report engagement in outdoor activities and exposure to parasites if questioned accordingly. Of note, exposure to parasites may also occur indoors, particularly if patients keep pets or maintain low hygiene standards. The latter may be associated with ongoing exposure to parasites and thus, clinical examination of the patient may reveal more recent bites.

Urticaria is a very common, unspecific symptom and may be evoked by a variety of conditions, e.g., administration of drugs, infectious diseases, infestation with intestinal parasites and physical stress [11]. Thus, anamnesis as well as subsequent general examination should aim at ruling out these differential diagnoses. With regards to drug administration, recently initiated or changed medication is most likely to trigger such a reaction. However, patients may present new side effects even after having tolerated a certain therapy for years.

Laboratory analyses of blood samples are not indicated unless previous findings point at an underlying primary disease or systemic involvement [12]. This also applies for histopathological analyses of skin biopsies.

Similarly, further diagnostic measures are recommended if papules persist for more than six weeks.

• Sarcoptes Scabiei

  Papular urticaria is diagnosed in patients of appropriate age with symmetrically distributed lesions, a history of hypersensitivity, and exposure to animals or insects. 7 Scabies is caused by the Sarcoptes scabiei mite and is spread through skin-to-skin [aafp.org]

Treatment of PU is supportive. Topical application of antihistamines or corticosteroids may be considered and should induce involution of papules and provide rapid relieve from pruritus. In cases of extensive lesions, systemic use of such drugs may be indicated. However, neither of both types of administration is suitable for long-term use. Thus, it is of utmost importance to identify the source of insect or arachnid bites and to take appropriate measures to eliminate it.

Topical or systemic administration of antibiotics may be required to treat secondary bacterial infections.

Papules and pruritus may recur in warm summer months of several years during childhood, but long-term prognosis is very good. Patients finally develop tolerance to insect and arachnid bites, a process presumably mediated by desensitization, and symptoms rarely persist into adulthood.

PU-associated papules are generally thought to be the result of a hypersensitivity reaction to insect or arachnid bites. Whereas wheals developing at the site of mosquito or flea bites, for instance, are provoked by active injection of anticoagulants into the human skin, this is not necessarily the case in PU. The mere contact with the animal seems to be sufficient to induce hypersensitivity and PU has been described to occur after exposure to Dermestes maculatus and caterpillars [2] [3]. In rare cases, PU does not seem to be related to exposure to any arthropods [4].

The following animals have been suggested or proven to cause PU:

• Fleas
• Bed bugs
• Mosquitoes
• Midges
• Other flies
• Caterpillars
• Mites
• Ticks
• Other arachnids

Fleas seem to be of particular importance in this context. One study describing 20 cases of PU found fleas to be responsible for all these cases [5].

Relapses of PU can best be prevented by identifying and eliminating or avoiding the trigger of the disease. However, this may not be an easy task and in some cases, general measures are more effective and the etiologic agent is not identified.

Because PU is triggered by exposure to insects and arachnids, there is a strong spatiotemporal correlation between PU incidence and parasite presence. In this context, it is little surprising to detect higher PU incidence rates in geographical regions marked by hot and humid climates and during seasons characterized by these same conditions [6]. Moreover, the climate phenomenon El Niño does not only account for elevated water and air temperatures but also for an increased incidence of PU [7].

No predilection regarding race or gender has been suggested.

The majority of PU patients are children aged less than 10 years. On the one hand, this may be due to little awareness of parasites in their surroundings and consequently increased exposure. On the other hand, there is evidence suggesting that children are generally more susceptible to PU than adults. An adult's immune system seems to provide certain protection against PU and the disease is rarely diagnosed in the respective age group.

According to current knowledge, a type I hypersensitivity reaction accounts for PU. This type of allergy requires repeated exposure to certain antigens and sensitization of mast cells. With regards to insect and arachnids inhabiting the surroundings of PU patients, this situation is easily conceivable. Antigens may be introduced into the patient's circulation during an insect or arachnid bite, although plasma cells and mast cells are less likely to encounter antigens of parasites that don't bite. The fact that papules often form at a considerable distance from insect bites supports the theory of systemic pathomechanisms. Specific antigens that trigger PU have not yet been identified.

Histopathological analyses confirm the hypothesis of an immune-mediated process. Mononuclear and polynuclear cell infiltrates predominate in dermal layers, but inflammatory cells may also migrate into the epidermis. Further, characteristic, but not specific findings are mild acanthosis, spongiosis and subepidermal edema [8]. While immunoglobulin deposits could not be detected in the previously cited study, different findings have been reported several years ago [9].

Such deposits would indicate a type III hypersensitivity reaction. The latter may induce urticarial vasculitis, but this disease generally comprises larger areas of the skin than PU and instead of small papules, more extensive lesions develop.

Type I and type III hypersensitivity additionally differ regarding involved subclasses of immunoglobulins. While type I hypersensitivity reactions are mainly mediated by IgE, immunocomplexes formed during a type III reaction principally contain IgG. A recent publication reports antibody profiles to vary with the duration of the disease, but found a general predominance of IgE in patients suffering from PU [10]. These results further support the hypothesis of a type I hypersensitivity reaction to provoke skin lesions in PU.

Exposure to insects and arachnids can be significantly reduced by applying the following measures:

• Pets should be treated regularly with antiparasitic compounds. Such drugs should be obtained at a veterinarian's and not at the local supermarket.
• Bedding and clothes should be aired, washed and, if necessary, replaced, to maintain an adequate hygiene standard.
• When engaging in outdoor activities, long-sleeved clothes should be worn and repellents should be used. Caution should be exercised when treating children with repellents and only such products recommended for this age group should be used.

Papular urticaria (PU) is a common disorder mostly diagnosed in children. PU patients typically present with multiple papules and pruritus that are thought to be the result of a hypersensitivity reaction to insect or arachnid bites [1]. Of note, PU-associated sublime lesions do not correspond to insect bites themselves and may form at a considerable distance from the initial lesion. Unlike true urticaria, a condition provoked by exposure to allergens, nettles etc., PU persists for several days or even weeks.

Patients, particularly pediatric patients, may be greatly bothered by pruritus, may scratch papules and cause deeper injuries. Secondary bacterial infection of the latter may aggravate skin damage. This may require specific treatment and lesions may not heal without leaving scars. In general, PU-associated lesions don't break, don't pose a risk of infection and undergo spontaneous remission.

Because in the vast majority of cases, PU is associated with arthropod exposure, prevention of the latter may contribute to avoid the former. Thus, appropriate measures should be taken to reduce parasitic infestation of pets, to diminish parasitic loads in bedding and clothes, and to prevent exposure to those parasites that typically accompany outdoor activities. Indeed, analysis of epidemiological data revealed an increased incidence of PU during summer months, the time of the year at which people are mostly engaged in outdoor sports and recreation.

Although recurrent PU is frequently observed, the disease is generally self-limiting. Topical application of antihistamines or corticosteroids may provide relieve from severe pruritus. Otherwise, pharmacological treatment is only required if deep scratches aggravate skin damage.

Urticaria is the medical term used to describe itching wheals that generally develop upon exposure to an allergen, contact with nettles etc. Such dermatological alterations usually subside after short periods of time. Patients suffering from papular urticaria (PU) show similar sublime, reddened skin lesion that do, however, persist for days or even weeks.

Causes

According to current knowledge, PU is triggered by a type I hypersensitivity reaction to parasitic antigens, i.e., papules form due to an immune reaction similar to that one observed during an allergy test. A wide variety of parasites, namely insects and arachnids, have been suggested or proven to cause PU:

• Fleas, ticks and mites that usually infest pets
• Bed bugs
• Mosquitos, midges
• Caterpillars

Consequently, in order to avoid PU, pets should be regularly treated with antiparasitic drugs, an appropriate hygiene should be kept regarding bedding and clothing, and preventive measures should reduce the risk of insect bites while engaging in outdoor activities.

Symptoms

Multiple, clustered papules and pruritus are characteristic for PU. While these lesion may form in close proximity to an insect or arachnid bite, they may also develop at a considerable distance from it. Exposed skin is affected more frequently, but PU may affect any area of the body. Skin alterations persist for several days and in the course of disease, papules emerge, merge, subside and emerge again.

Most PU cases are diagnosed in summer months in geographical regions marked by warm and humid climates. Skin lesions often resolve in winter, but may reappear the following year.

Diagnosis

Anamnesis and dermatological findings are the basis of PU diagnosis. Additional exams are rarely required, but may be realized if doubts remain and differential diagnoses need to be ruled out. Such exams may comprise laboratory analyses of blood and urine samples as well as skin biopsies.

Treatment

Symptoms associated with PU may be treated with antihistamines or corticosteroids; both may be applied topically or systemically. They induce involution of papules and provide rapid relieve from pruritus. However, they are not suitable for long-term therapy. It is therefore of utmost importance to identify the source of insect or arachnid exposure and to eliminate it.

Of note, antibiotics may be required if deep skin lesions, usually resulting from scratching due to intense pruritus, show signs of secondary bacterial infection.

1. Stibich AS, Schwartz RA. Papular urticaria. Cutis. 2001; 68(2):89-91.
2. Rustin MH, Munro DD. Papular urticaria caused by Dermestes maculatus Degeer. Clin Exp Dermatol. 1984; 9(3):317-321.
3. Demain JG. Papular urticaria and things that bite in the night. Curr Allergy Asthma Rep. 2003; 3(4):291-303.
4. Bronstein DE, Cotliar J, Votava-Smith JK, Powell MZ, Miller MJ, Cherry JD. Recurrent papular urticaria after varicella immunization in a fifteen-month-old girl. Pediatr Infect Dis J. 2005; 24(3):269-270.
5. Naimer SA, Cohen AD, Mumcuoglu KY, Vardy DA. Household papular urticaria. Isr Med Assoc J. 2002; 4(11 Suppl):911-913.
6. Howard R, Frieden IJ. Papular urticaria in children. Pediatr Dermatol. 1996; 13(3):246-249.
7. Andersen LK, Davis MD. The effects of the El Nino Southern Oscillation on skin and skin-related diseases: a message from the International Society of Dermatology Climate Change Task Force. Int J Dermatol. 2015; 54(12):1343-1351.
8. Jordaan HF, Schneider JW. Papular urticaria: a histopathologic study of 30 patients. Am J Dermatopathol. 1997; 19(2):119-126.
9. Heng MC, Kloss SG, Haberfelde GC. Pathogenesis of papular urticaria. J Am Acad Dermatol. 1984; 10(6):1030-1034.
10. Cuellar A, Rodriguez A, Halpert E, et al. Specific pattern of flea antigen recognition by IgG subclass and IgE during the progression of papular urticaria caused by flea bite. Allergol Immunopathol (Madr). 2010; 38(4):197-202.
11. Zuberbier T, Asero R, Bindslev-Jensen C, et al. EAACI/GA(2)LEN/EDF/WAO guideline: management of urticaria. Allergy. 2009; 64(10):1427-1443.
12. Kozel MM, Bossuyt PM, Mekkes JR, Bos JD. Laboratory tests and identified diagnoses in patients with physical and chronic urticaria and angioedema: A systematic review. J Am Acad Dermatol. 2003; 48(3):409-416.