The prevalence of skin diseases

Created 2008.

Learning objectives

• Participants should be familiar with the prevalence of skin diseases in the New Zealand community

Introduction

There has not been much research data published on the prevalence of skin diseases in New Zealand. In general, the disorders seen in general practice and dermatology clinics are similar in scope to other Western countries. However, the reported incidence of skin cancer and related disorders is much greater in Australia and New Zealand than in the United Kingdom, presumably primarily because of high environmental exposure to ultraviolet radiation.

In survey of patients seen in outpatients in Auckland in 1984, the most common conditions seen were cutaneous malignancies (20%), actinic keratoses (17%), and eczema (17%).¹

An analysis of hospital attendances for skin diseases conducted in Perth in 1992 reported the most common conditions encountered were actinic keratoses, psoriasis, malignant tumours and dermatitis.²

The range of skin conditions seen by dermatologists depends on:

• The actual prevalence of skin disease
• The potential clinical morbidity and mortality of the disease
• The clinical severity of the disease in the individual
• Ethnicity and skin colour
• The availability of effective therapy
• The impact on the individual (employment, educational and psychosocial effects)
• Public awareness and concern (especially relating to skin cancer)
• The referring doctor's interest and knowledge about skin disease (increased knowledge may increase or reduce referral numbers)
• Availability of diagnostic and treatment services
• Cost of diagnostic and treatment services

Skin disease prevalence in the community is largely unknown. Several population surveys have been carried out in the Maryborough community in Victoria, Australia. Light exposed sites were examined in 2113 adults in a 1983 report; 49 (2.32%) had at least one skin cancer and 1202 (56.9%) had at least one actinic keratosis.³ Total body examinations in 1457 adults was reported in 1999. The age- and sex-adjusted prevalence of warts was 7.1%, acne 12.8%, atopic dermatitis 6.9%, seborrhoeic dermatitis 9.7%, asteatotic dermatitis 8.6%, psoriasis 6.6%, culture-positive tinea 12%, seborrhoeic keratoses 58.2%, and Campbell de Morgan spots 54.4%.⁴ Subsequent examination of a sample of the non-respondents revealed they were more likely to have skin cancers and Campbell de Morgan angiomas than the respondents. The authors comment that as population-based surveys on the frequency of common skin diseases rely on voluntary presentation, there is a risk of response bias which may compromise the quality of the data obtained.⁵

Some skin disorders are more common in those with black skin (tinea capitis in children and acne keloidalis nuchae in adults for example)⁶ and others less common (skin cancer).

A significant percentage of the workload of a general practitioner is dermatological. A study of a practice in Cornwall published in 1999 found 21% of 11,191 patients seen had a dermatological diagnosis (21%). The most common skin diseases seen were viral warts, eczema and benign tumours.⁷ Skin disease is not simply a cosmetic problem and may have similar impact to other medical disorders. Dermatologic problems can result in psychosocial effects that seriously affect patients' lives comparable to arthritis and other disabling illnesses.⁸

Infections

Cutaneous infections are remarkably common, with 109 of 300 consecutive patients seen in Auckland Hospital dermatology clinic demonstrating culture positive erythrasma or tinea pedis.⁹

Although less common in children than in adults, culture positive tinea pedis was found in 5.2% of 2491 students in Victoria. There was a rising prevalence with age.¹⁰

Inflammatory dermatoses

Ninety-one percent of males and 79% of females attending 6th and 7th form classes in Auckland were reported in 1995 to have some acne. Severe acne was present in 6.9% males and 1.1% females.¹¹

The prevalence of acne ranged from 27.7% in 10-12 year olds to 93.3% in 16-18 year olds in a study of 2491 students in Victoria. Treatment for many of these was classified as being likely to have no beneficial effect.¹² The prevalence of atopic dermatitis based on examination of these students was 16.3%. ¹³ The same group also examined 1116 children under 5 and found the prevalence of atopic dermatitis was 30.8%.¹⁴ Other skin problems detected in these children included seborrhoeic dermatitis (10%) and pityriasis capitis (41.7%) and were most common in the first 3 months of life.¹⁵

Skin cancer

New Zealand Health Information Service provisional cancer statistics for 2003 include 248 deaths and 1842 registered cases of melanoma.¹⁶ There were a similar number of cases of melanoma in situ.

A review of cutaneous melanoma in Caucasian New Zealanders 1995-1999 concluded: ‘New Zealand continues to have one of the highest rates of melanoma in the world, with an increasing Breslow thickness of melanoma (P < 0.001) over the 5-year period. Men have a higher rate and deeper melanomas than women (P < 0.001). The incidence of melanoma appears to have reached a plateau over the review period. The far north of New Zealand (Whangarei and further north) had the highest rate of melanoma in New Zealand (59.1/100000, age standardised) and the lowest rate is in Southland (23.5/100000).’¹⁷

The rates of non-melanoma skin cancer in New Zealand are difficult to determine as registration is not required and many of these lesions are treated by cryotherapy or other destructive measures without histological confirmation. A survey of skin cancer incidence in the Hamilton area published in 1982 reported an incidence of 384/100,000 of non-melanoma skin cancer and melanoma rate of 23/100,000¹⁸. In 2002 unpublished data indicated the rates may be at least double those of the 1982 study (personal communication). A study of the Maryborough population in New South Wales (Australia) that was reported in 1989, showed a calculated minimal age-standardised incidence rate of 873 non-melanocytic skin cancers/100,000 population each year.¹⁹

Activity

Do a Medline search to find reports of diagnostic accuracy for skin diseases. What proportion of referred patients have an incorrect diagnosis made by the general practitioner?