Itch represents a cardinal feature of many skin and systemic diseases1–4. Although we do have some insights into the epidemiology of itch5,6, limited work is ongoing in understanding the impact of itch across entire populations. If a patient seeks out health care services for a condition or a symptom, one can hypothesize that this constitutes prima facie evidence that there is meaningful impact upon the individuals who receive care. In 2013, Shive et al7 published results from the cross-sectional National Ambulatory Medical Care Survey (NAMCS) for itch as a symptom during the interval from 1999 to 2009. This seminal work was performed in the United States. These workers found interesting demographic and disease-related predictors of itch as a symptom.
The present study extends the scope of this earlier analysis, and in doing so utilizes a longer study interval and somewhat different analytic approaches to add to this earlier work. A goal was to estimate the degree of under-reporting of itch and thus to predict a more realistic estimate of visits with itch.
Data from the 1993 to 2015 NAMCS, from the Centers for Disease Control and Prevention (CDC) were used to characterize outpatient visits for itch. These surveys were developed and implemented by the National Center for Health Statistics, part of the CDC8. Results from the survey provide nationally representative yearly estimates of non–hospital-based outpatient health care utilization. As a brief overview of how the NAMCS survey data are collected, using a list of all medical doctors and doctors of osteopathy, a sample of physicians are selected and invited to participate in the annual survey. For participating physicians, data were recorded for a sample of their visits for a random week of the year. To account for the variance caused by the complex survey design, and for all analyses we used survey weights to provide the more precise estimates.
Itch visit identification
Studied in this analysis were itch symptom visits. This study used virtually the same methods as Shive et al7. In this regard, we identified the reason for visit codes ordered first through fifth, for all reasons in which the word “itching” appears, including 1340.2 (eyelid itching), 1365.1 (ear itching), 1605.4 (anal/rectal itching), 1715.4 (scrotal itching), 1765.3 (vaginal itching), 1770.1 (vulvar itching), 1870.2 (skin itching), and 1890.4 (scalp itching). In addition, the analysis included a diagnosis if itching is intrinsic to a diagnosis as listed in the International Classification of Diagnoses, Ninth edition, Clinical Modification9 (ICD-9-CM) including: 698.0 (pruritus ani), 698.1 (pruritus of genital organs), 698.2 (prurigo), 698.3 (lichenification and lichen simplex chronicus), 698.8 (other specified pruritic conditions), and 698.9 (unspecified pruritic disorder).
We defined seasons using meteorologically defined seasons: March 1 to May 31 is spring, June 1 to August 31 is summer, September 1 to November 30 is fall, and December 1 to February 28 is winter10. Through the entire study period, NAMCS allows for recording up to 3 diagnoses (primary, secondary, and tertiary). To decrease the likelihood of bias, when examining diagnoses, this component of the study was limited to visits at which there was one and only one diagnosis.
Other analytic details
Over the entire study interval, there were a small number of visits at which patients with races other than white, African American, and Asian were observed. Because of the relative unreliability of the estimates associated with these small numbers, other designated races (Native Hawaiian or Other Pacific Islander, American Indian or Alaska Native, and more than one race reported) were not included in the analysis.
In order to estimate under-reporting of itch as a symptom, the leading 5 rank-order diagnoses were evaluated for the proportion of visits at which itch was reported. An exception to this is the ICD-9-CM code series 698.0–698.9, in which itch is a given as part of the diagnosis. Analyses were performed using SAS University Edition and using the weighted SURVEY procedures which utilize individual patient weights to provide nationally representative estimates. Unless otherwise stated, all numbers reported represent weighted estimates. Hypothesis testing was performed with SURVEYFREQ and SURVEYREG, which take into account the variability associated with the complex sampling frame. Significance was defined as being achieved when P<0.05.
Over the 23-year study interval, there were a total of 641,861 visits estimating the experience of 17.6 (95% confidence interval: 17.6, 17.6) billion visits. This analysis finds 4661 visits estimating the experience of 129 (123, 134) million itch visits occurred, averaging 5.61 million visits per year, The proportion with itching was estimated to be 0.72% (0.69%, 0.76%). The proportion of females with itch at 0.84% (0.80%, 0.88%) was higher than for males 0.57% (0.53%, 0.61%) (P<0.0001). The proportion of people by race presenting with itch was examined. In this regard, Asians proportionately were most likely to present with itch 1.3% (1.1%, 1.6%) whereas African Americans were less likely at 0.99% (0.85%, 1.3%) and whites were least the likely at 0.67% (0.64%, 0.71%) (P<0.0001).
All specialties of physicians had fewer than 1% of their patients experiencing itch, except for dermatologists at 4.8% (4.5%, 5.1%) and obstetrics and gynecology at 1.4% (1.2%, 1.5%).
A pattern of monthly and seasonal variability in the likelihood of itch visits was observed. The lowest likelihood month was December whilst the highest likelihood month was June (Fig. 1, P<0.0001). Similarly, the lowest likelihood season was winter whilst the highest likelihood season was summer (Fig. 2, P=0.0002).
The mean age of itching patients was 45.3 (44.4, 46.3) years. However, the distribution of ages was not uniform, with a higher proportion occurring in those aged at least 70 years old, and this distribution is presented in Figure 3.
The 5 most common diagnoses in which itching is reported are dermatitis not otherwise specified, vaginitis and vulvovaginitis, candidiasis of the vulva and vagina, unspecified pruritic disorder, and atopic dermatitis. These are presented in Table 1. Note that in this paper these are defined as itching conditions, yet the rate at which the symptom was reported varied from 13% to 71%. Of note, the diagnosis of atopic dermatitis has itching reported in less than one fifth, which must represent a systematic under-reporting process. In order to maintain the highest reliability of estimates, further rank-order reporting of itching diagnoses is limited.
The 3 leading itching diagnoses by season varies but always includes dermatitis not otherwise specified and vaginitis and vulvovaginitis (Table 2). Interestingly, in winter, urticaria becomes one of the 3 leading diagnoses. Again, because of insufficient sample size, reporting additional diagnoses becomes increasingly unreliable.
Although the current study uses approximately twice the years of study, the results reported in this manuscript are similar to the results reported by Shive et al7. As the methods for defining an itch visit were nearly identical, this outcome is to be expected. Whereas their group estimated 7 million itch visits per year, the present study arrives at 5.6 million per year, evidence of remarkable stability in the data. As their group also states, less than half the itching population will present to physicians for care7. Thus, estimates contained in this investigation represent only those with sufficient burden or financial means to seek care.
However, many of the investigations were different. For instance, the demonstration of the peak number of itch visits in June and thus summer and the nadir in December and thus winter has not been previously demonstrated. There are few investigations into seasonality of any skin disease11,12, and further work into this area is needed to help understand the potential causes. There is some seasonality in the presentation of itching diagnoses and this has had no exploration. An interesting example of this is the finding that urticaria appears in the leading 3 diagnoses in the winter but not any other season. Few have examined the role of seasonality in urticaria, but it has been linked with seasonal exacerbation of asthma13. Others have reported spring14 and summer15 exacerbations of urticaria, but none in the winter. The reason for these differences remain unclear.
An additional point is noteworthy regarding vulvovaginal conditions including candidiasis and vaginitis and vulvovaginitis are commonly associated with itching, yet under-represented in the dermatology literature. Since 1998, there have been 68 publications for vulvovaginal candidiasis and itch or pruritus, but only 4 of these are published in dermatology journals. As a result, there may be a more substantial itch burden in women’s genitalia than the dermatology community recognizes.
In addition, in terms of our demographic findings, elderly people are observed to constitute a reasonably large proportion of the population presenting for itch visits. The itching of this population has been addressed in previous works16,17, and remains a meaningful burden.
The most important limitation of this analysis is that many other diseases itch, yet are not explicitly captured. The data for the NAMCS are collected by health care providers, and they record the patient experience from their perspective. Accordingly, patient-reported outcomes such as itch, pain, nausea, fever, and other symptoms are not likely as accurately captured as other data. The advantage of the data is that it in large, cross-sectional manner collects data from multiple geographic locations and physician specialties.
This paper presents an updated and expended understanding of ambulatory, office-based care for itching in the United States. Reported visits for itching must represent scratching the surface and not a complete picture of the total burden of disease.
IRB statement: human data were deidentified from CDC public use datasets.
Source of funding
This article has no direct funding source.
Conflicts of interest statement
A.B.F. was formerly employed by AbbVie Inc. He has no other potential conflicts including Honoraria, Speakers bureau, Stock ownership or options, Expert testimony, Grants, Patents filed, received, pending, or in preparation, Royalties, or Donation of medical equipment.
The author thanks SAS Institute for providing University Edition software access for scholarly research.
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