Pigmentary disorders are frequently encountered in dermatologic practice. Asian patients are generally anxious when pigmentary changes occur, as these disorders tend to be more pronounced in pigmented skin.
While many pigmentary disorders encountered may be benign in nature, the impact on the patient’s sense of wellbeing and quality of life is often significant (see also Chapter 23). There are also situations where alterations of skin pigmentation indicate underlying systemic disease, which the clinician should be aware of.
The clinician should be familiar with the more common pigmentary disorders and understand their basic pathophysiology in order to administer the appropriate treatment. More importantly, the clinician needs to recognize when a pigmentary alteration suggests an underlying systemic illness or malignancy. In addition, several pediatric genodermatoses (see also Chapter 8) associated with pigmentary alterations may be complicated by systemic involvement, which should be evaluated for.
BASIC PHYSIOLOGY OF THE PIGMENTARY SYSTEM
Pigmentation in the skin is the result of melanin in the keratinocytes. The primary function of melanin is to protect the skin from damage induced by ultraviolet (UV) light. Melanin is produced by melanocytes and these are cells derived from the neural crest which migrates to the skin during embryogenesis where they end up in the basal layer of the epidermis. Other than the epidermis, these specialized cells are also found in the hair matrix, stria vascularis of the ear, retina of the eye, as well as in the leptomeninges.
Melanocytes produce melanin, and these are packaged into melanosomes which are then transferred to keratinocytes where they provide protection for the keratinocytes from UV rays and give the skin its distinctive color.
There are essentially two types of melanin produced by the melanocytes: the darker brown eumelanin and pheomelanin, which gives skin a more yellow and red coloration. Variations in skin color in different races are partly due to these different types of melanin with the Caucasian population having more pheomelanin, resulting in the fair skin, red hair phenotype. Asians tend to have more eumelanin, resulting in the brown skin, black hair phenotype. In terms of the actual numbers of melanocytes in the epidermis, there is no difference between Caucasians and Asians. The difference in perceived skin color is mainly due to the type of melanin present, the amount of melanization in melanosomes, as well as the number, and distribution of melanosomes within the keratinocytes.
CLINICAL APPROACH TO PIGMENTARY DISORDERS
Pigmentary disorders occur due to either loss of melanocytes, increase or decrease in melanocyte activity. As such, pigmentary disorders are commonly divided into two broad categories: (1) hyperpigmentary disorders resulting from increased melanocyte activity and (2) hypopigmentary disorders resulting from decreased melanocyte activity or actual loss of melanocytes. The morphologic classification and approach to pigmentary disorders is usually based on the type, number, ...