Chapter 21: Pigment Disorders

INTRODUCTION TO CHAPTER

Although disorders of pigmentation are not life-threatening, their impact can be profound. Lack of pigment or excessive pigment is quickly noticed by others and can create psychological stress for affected individuals. This is even more important during the sensitive years of adolescence, when many of these disorders begin. Depression, anxiety, embarrassment, seclusion, low self-esteem, fear of rejection, and perception of discrimination may occur in these patients. Additionally, the stigma associated with pigmentary disorders in certain cultures can cause an even greater psychological impact. Clinicians should be aware of these issues as well as the diagnosis and treatment of pigmentary disorders when treating affected patients.

VITILIGO

Introduction

Vitiligo, one of the most common pigmentary disorders, affects 0.5% to 1% of the world's population without discrimination based on gender, age, location, or race. Women and those with darker skin may be more likely to present to medical attention. Most affected individuals develop lesions before 20 years of age and experience a progressive increase in depigmentation over time. The disease is multifactorial but ultimately results in loss of melanocytes, causing disfigurement, sun sensitivity, and severe psychosocial distress.¹ For these reasons, it should be thought of as more than a purely cosmetic disorder and recognized for its real effects on patient health.

Pathophysiology

Research into the pathogenesis of vitiligo is an active field, but has not yet resulted in a clear answer. Several mechanisms have been proposed, such as genetic abnormalities, autoimmunity, and dysregulation of redox (reduction–oxidation), biochemical, and neural pathways, all of which culminate in the common endpoint of melanocyte destruction.² Vitiligo is considered an autoimmune disease for several reasons.³ First, it is associated with other autoimmune disorders (particularly autoimmune hypothyroidism, pernicious anemia, Addison's disease, and systemic lupus erythematosus). Second, elevated levels of autoantibodies not only directed at melanocytes, but also at other end organs (thyroid, gastric mucosa, adrenal gland, etc.) are often found in affected individuals. Additionally, cytotoxic T cells infiltrate active lesions, clearly implicating the immune response in disease activity. Interestingly, vitiligo sometimes develops in patients who successfully mount an immune response to malignant melanoma, and has even been observed following bone marrow transplantation from an affected donor.⁴

Controversy exists as to whether autoantibodies and immune system activation are the precipitating event or a response to melanocyte death from other causes in patients with vitiligo.⁵ For example, impaired handling of oxidative stress is observed in affected patients, leading to cell death. Affected skin may be more susceptible to cell loss through apoptosis and via melanocytorrhagy, which is the upward migration and loss of melanocytes through the stratum corneum due to inadequate cell adhesion.

The distribution of segmental vitiligo is in a quasi-dermatomal pattern, leading to the hypothesis that neural factors are important in the development of this form ...