Psoriasis is widely distributed all over the world with fluctuations in prevalence amongst certain races and countries.
Psoriasis is one of the oldest skin diseases known to medical science, though the history of psoriasis makes an interesting reading as it had been mistaken for other diseases, especially leprosy, till about 150 years ago.
How Common is Psoriasis?
Genetic and environmental factors play an important role in the clinical development of psoriasis. This in turn affects how persons of different ethnic groups are affected by psoriasis and how common psoriasis is in different parts of the world.
Patients may not approach doctors for minor forms of the disease. In many developing countries, poverty, illiteracy, or ignorance may prevent patients from approaching doctors; worse still, may be getting treated by quacks. In many countries modesty prevents females from seeking medical assistance for skin diseases. Many cases of psoriasis may be misdiagnosed for contact dermatitis and eczema by general practitioners who do not have adequate training in skin diseases. Hence psoriasis may be much more prevalent than the present studies suggest.
Estimates of the occurrence of psoriasis in different parts of the world vary from 0.1 to 3%. Thus it is estimated that around 125 million people worldwide have psoriasis. 10-30% of people with psoriasis go on to develop psoriatic arthritis, a debilitating type of inflammatory joint disease.
According to the National Institutes of Health (NIH), between 5.8 and 7.5 million, i.e. between 2 and 2.6% of the population, is affected with psoriasis in the US. Around 150,000 new cases of psoriasis are reported annually. Four hundred people die annually from psoriasis-related causes in the US.
Geographical and Racial Distribution of Psoriasis
The incidence of psoriasis is much lower in dark-skinned West Africans and African-Americans than in light-skinned people of European ancestry. Incidence is also low in Japanese and Eskimos, and is extremely low to non-existent in Native Americans in both North and South America.
The prevalence of psoriasis in African Americans has been estimated at 0.7% based on 3860 consecutive patients seen in a private dermatology practice in Cleveland, Ohio.
In Africa, variations in the prevalence of psoriasis have been observed between West African countries such as Nigeria (0.8%) and East African countries such as Kenya (2.6%).
Age of Onset in Psoriasis
Psoriasis occurs in both children and adults and may appear at any age, although it is most commonly diagnosed between the ages of 12 and 35. A second peak appears between the ages of 60 to 69 years.
There have also been case reports of psoriasis appearing in infants within weeks of birth and in patients above the age of 70 years, but these are more of exceptions rather than the rule.
Approximately 10-15% of new cases begin in children younger than 10 years. Children tend to have more of the guttate variety of psoriasis than the plaque psoriasis compared to adults. The median age at onset of psoriasis is 28 years.
Females tend to develop psoriasis slightly earlier than males and those with a family history have an early age of onset.
Sex Incidence in Psoriasis
Psoriasis occurs with almost equal frequency in males and females. Many studies have found higher prevalence among males while others vouch for a higher female prevalence. As the difference between the genders is not very prominent, we will settle for the equal frequency.
There may be another reason for the disparity in sex prevalence studies.
As females are more concerned about the condition of skin and nails and are more aesthetically inclined than their counterparts, they may be approaching doctors more often with milder varieties of psoriasis.
Next: Causes of Psoriasis and Psoriasis Skin Changes.
References
- National Psoriasis Foundation Stats
- Various Text Books and Journals of Dermatology
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