Skin prick test for the evaluation of patients with idiopathic generalized pruritus: preliminary results

Pruritus is the unpleasant sensation that leads to scratching and irritation of the skin [1]. Pruritus may be generalized or localized [2]. It is one of the most common subjective symptoms in dermatology. Pruritus lasting more than six weeks is called chronic pruritus. The prevalence of chronic pruritus in the general adult population has been reported 13.5%, recently [1]. It has been suggested that 60% of the elderly individuals aged 65 and over suffer from moderate or severe pruritus [1]. However, the prevalence of pruritus in elderly varies in studies. Goyal et. reported that pruritus was observed in only 5% of the patients aged 60 and above [3]. Pruritus can decrease the patient’s quality of life by leading to anxiety, sleep disturbances, sexual dysfunction and attention problems [1]. Pruritus usually occurs as a result of dermatological conditions like xerosis and eczema [4]. However, various systemic disorders including diabetes mellitus, cholestasis, uremia, thyroid disorders, iron deficiency, polycythemia vera, essential thrombocytosis, malignancy, human immunodeficiency virus infection, hepatitis C infection and drug reactions may be the underlying cause of pruritus [2,4]. It has been suggested that a systemic etiology can be detected in 14% to 24% of patients complaining of generalized pruritus without any primary cutaneous cause [5].


INTRODUCTION
Pruritus is the unpleasant sensation that leads to scratching and irritation of the skin [1].Pruritus may be generalized or localized [2].It is one of the most common subjective symptoms in dermatology.Pruritus lasting more than six weeks is called chronic pruritus.The prevalence of chronic pruritus in the general adult population has been reported 13.5%, recently [1].It has been suggested that 60% of the elderly individuals aged 65 and over suffer from moderate or severe pruritus [1].However, the prevalence of pruritus in elderly varies in studies.Goyal et. reported that pruritus was observed in only 5% of the patients aged 60 and above [3].Pruritus can decrease the patient's quality of life by leading to anxiety, sleep disturbances, sexual dysfunction and attention problems [1].
Pruritus usually occurs as a result of dermatological conditions like xerosis and eczema [4].However, various systemic disorders including diabetes mellitus, cholestasis, uremia, thyroid disorders, iron deficiency, polycythemia vera, essential thrombocytosis, malignancy, human immunodeficiency virus infection, hepatitis C infection and drug reactions may be the underlying cause of pruritus [2,4].It has been suggested that a systemic etiology can be detected in 14% to 24% of patients complaining of generalized pruritus without any primary cutaneous cause [5].
Detailed medical history of patients with chronic pruritus is required to determine the etiology.Diagnostic assessment should include clinical characteristics of pruritus, presence of cutaneous lesions, previously diagnosed systemic and dermatological diseases, family history, medications, allergies, and susceptibility to atopic dermatitis [6].Evaluation of laboratory tests including complete blood count, liver function tests like alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase, blood urea nitrogen, serum creatinine, ferritin and thyroid-stimulating hormone levels is recommended in patients without any dermatological and physical findings [4,7].However, in 8% of all patients complaining of pruritus, no underlying dermatosis or systemic disorder can be detected.This condition is termed as idiopathic generalized pruritus [7,8].
Hereby, we report the skin prick test results of the patients who had generalized pruritus without any underlying disorder or primary skin lesions.

MATERIALS AND METHODS
Medical reports of the patients with idiopathic generalized pruritus who were admitted to dermatology outpatient clinic between April 2017 and May 2018 were reviewed retrospectively.The exclusion criteria were pregnancy, malignancy, renal failure, use of systemic antihistamines, corticosteroids, tricyclic antidepressants, mast cell stabilizers and immunosuppressive drugs within four weeks.
The skin prick test was made on the flexural surfaces of the forearms (Figure 1).The test area was disinfected with 70% ethanol.
Allergen solutions were placed on the flexural surfaces of both forearms at a two cm distance from each other.Small pricks were made into the skin through allergen extract drops using disposable plastic lancet.The excess solutions were removed gently using a paper towel to prevent the mixing of allergens with each other.The results were evaluated 15 minutes after the skin pricks.Allergen reactions were considered positive when the wheal diameter was 3 mm or larger than the negative control (Figure 1).
The past medical history was remarkable for angioedema in one patient, rosacea in one patient, allergic rhinitis in two patients and hyperlipidemia in two patients.Seven

DISCUSSION
Skin prick test is a quick, safe and minimally invasive method to detect reactions to food, drug, inhalant and occupational allergens [9].Skin prick test is usually performed to investigate the allergens in patients with rhinoconjunctivitis, contact urticaria, asthma, atopic eczema, and suspected food allergy [10].As the reaction to a specific allergen is localized, various allergens can be used at the same time.The prick test can be repeated to identify new sensitization in case of exposure to a new suspicious environmental allergen.Moreover, epidemiologic studies which determine sensitization rates in different areas contribute to create standardized allergen solutions [9].Most common aeroallergens are house dust mites, pet dander, pollens and moulds, whereas commonly detected food allergens in adults include shellfish, nut and fruit allergies [11].
The skin prick test results of the patients with idiopathic generalized pruritus have been reported in a few study.Sensitization to cobalt was reported to be a triggering factor for chronic pruritus [15].
In our study, skin prick test results of 18 patients with idiopathic generalized pruritus were reviewed.Most of the patients (61.1%) showed positive reaction to various allergen extracts.The most common allergies in Turkish patients were to trees mixture and Aspergillus mix.
The test result of a patient showed a positive reaction even to tea, which is frequently consumed in Turkey.Hereby, the preliminary results of skin prick test for the evaluation of patients with generalized pruritus have been reported.As our data increase, we would like to determine and share the most common allergens in Turkish patients with idiopathic generalized pruritus with our colleagues.

Statement of Human and Animal Rights
All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008.

Statement of Informed Consent
Informed consent was obtained from all patients for being included in the study.

Figure 1 :
Figure 1: Erythematous papules on the fl exor surface of the right forearm of the patient indicate a positive response.

Table 1 :
Allergen extracts used for the skin prick test

Allergens used for skin prick test
[12]ecen et al. reviewed skin prick test resultsof 190 patients with idiopathic generalized pruritus, atopic dermatitis, chronic idiopathic urticaria, alergic rhinitis and asthma.The study revealed that 28 of the 53 patients with idiopathic generalized pruritus (52.8%) had at least one or more positive reaction to the skin prick test.Banana, Dermatophagoides pteronyssinus and latex were the most common allergies in the group of idiopathic generalized pruritus.However, pine pollen, wheat pollen and dog epithelium were the most common allergies in all of the patients[12].

Table 2 :
The skin prick test results of the patients Patients