Vitiligo

Definition and Epidemiology

Definition

Vitiligo is a progressive skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions condition in which there is destruction of melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions resulting in the loss of skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions pigmentation.

Epidemiology

• Most common cause of depigmentation
• Prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency: 0.1%–2% of the general population
• Occurs in children and adults
• Equal incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency in males and females
• No racial or ethnic predilection
• Age:
  • Onset generally occurs before 30 years of age.
  • Peak incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency: 10–30 years of age

Etiology and Pathophysiology

Etiology

The cause of vitiligo is unknown, but is postulated to be a result of multiple factors.

• Possible genetic component: up to 50% of affected individuals have a family history Family History Adult Health Maintenance of the condition
• May be autoimmune mediated:
  • Approximately 20% of affected individuals have an autoimmune condition.
  • Associated conditions: 
    • Hashimoto’s thyroiditis Thyroiditis Thyroiditis is a catchall term used to describe a variety of conditions that have inflammation of the thyroid gland in common. It includes pathologies that cause an acute illness with severe thyroid pain (e.g., subacute thyroiditis and infectious thyroiditis) as well as conditions in which there is no clinically evident inflammation and the manifestations primarily reflect thyroid dysfunction or a goiter (e.g., painless thyroiditis and fibrous Riedel’s thyroiditis). Thyroiditis
    • Graves’ disease
    • Type 1 Type 1 Spinal Muscular Atrophy diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus
    • Addison’s disease
    • Pernicious anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types
    • Alopecia Alopecia Alopecia is the loss of hair in areas anywhere on the body where hair normally grows. Alopecia may be defined as scarring or non-scarring, localized or diffuse, congenital or acquired, reversible or permanent, or confined to the scalp or universal; however, alopecia is usually classified using the 1st 3 factors. Alopecia areata
    • Psoriasis Psoriasis Psoriasis is a common T-cell-mediated inflammatory skin condition. The etiology is unknown, but is thought to be due to genetic inheritance and environmental triggers. There are 4 major subtypes, with the most common form being chronic plaque psoriasis. Psoriasis
    • Inflammatory bowel disease
  • The presence of antibodies Antibodies Immunoglobulins (Igs), also known as antibodies, are glycoprotein molecules produced by plasma cells that act in immune responses by recognizing and binding particular antigens. The various Ig classes are IgG (the most abundant), IgM, IgE, IgD, and IgA, which differ in their biologic features, structure, target specificity, and distribution. Immunoglobulins: Types and Functions to melanin Melanin Insoluble polymers of tyrosine derivatives found in and causing darkness in skin (skin pigmentation), hair, and feathers providing protection against sunburn induced by sunlight. Carotenes contribute yellow and red coloration. Seborrheic Keratosis has been noted.
• Oxidative stress Oxidative stress A disturbance in the prooxidant-antioxidant balance in favor of the former, leading to potential damage. Indicators of oxidative stress include damaged DNA bases, protein oxidation products, and lipid peroxidation products. Cell Injury and Death
• Intrinsic defects of melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions

Pathophysiology

• Destruction, or disappearance, of melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions → loss of pigmentation in the affected area of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions
• This process gives the appearance of white patches on the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions.

Clinical Presentation and Diagnosis

Clinical presentation

Vitiligo results in hypopigmented or depigmented areas.

• Distribution: 
  • Widespread (generalized) with mucosal involvement
  • Segmental (entire body segments)
  • Localized
• Lesions’ appearance:
  • Sharply demarcated
  • Macules or patches
  • Milky or chalk-white color
• Most commonly affected areas: 
  • Face
  • Periorificial areas: 
    • Mouth
    • Anus
  • Genitalia
  • Elbows
  • Hands
  • Knees
• Hair in affected areas may also be depigmented.

Diagnosis

The diagnosis is usually clinical. However, the following examinations may be used if the diagnosis is unclear:

• Exam with a Wood’s lamp Wood’s lamp Malassezia Fungi:
  • Handheld device that emits ultraviolet (UV) A light
  • Useful in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with pale skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions where vitiligo lesions are more subtle
  • Accentuates hypo- or depigmented areas (appear white)
• Biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma: 
  • Can be used to differentiate from other hypopigmented disorders
  • Findings:
    • Absence of melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions
    • Loss of epidermal pigmentation
    • Perifollicular lymphocytic infiltrate may be seen in some patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship.

Management and Prognosis

General management and considerations

No cure is currently available. Management generally aims to slow the progression of the disease and address cosmetic issues.

• Basic measures:
  • All patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship should practice sun avoidance and protection.
  • Thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy function testing should be performed due to the strong association with thyroid Thyroid The thyroid gland is one of the largest endocrine glands in the human body. The thyroid gland is a highly vascular, brownish-red gland located in the visceral compartment of the anterior region of the neck. Thyroid Gland: Anatomy disease.
  • Counseling and other psychological intervention should be considered due to the effects of the disease on patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship‘ mental health and self-esteem.
• Choice of therapy depends on: 
  • Severity
  • Percentage of body surface area affected
  • Whether lesions are stable or progressive
  • Patient preference

Medical therapy

• Topical corticosteroids Corticosteroids Chorioretinitis: 
  • Useful in localized disease
  • Care should be used in sensitive areas due to the risk of skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation.
• Topical calcineurin inhibitors Calcineurin Inhibitors Compounds that inhibit or block the phosphatase activity of calcineurin. Immunosuppressants: 
  • Options: tacrolimus Tacrolimus A macrolide isolated from the culture broth of a strain of streptomyces tsukubaensis that has strong immunosuppressive activity in vivo and prevents the activation of T-lymphocytes in response to antigenic or mitogenic stimulation in vitro. Immunosuppressants, pimecrolimus Pimecrolimus Immunosuppressants
  • An alternative to topical steroids Steroids A group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. Benign Liver Tumors
  • Preferred in areas at high risk of skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation (e.g., skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions, genitals, intertriginous regions)
• Systemic glucocorticoids Glucocorticoids Glucocorticoids are a class within the corticosteroid family. Glucocorticoids are chemically and functionally similar to endogenous cortisol. There are a wide array of indications, which primarily benefit from the antiinflammatory and immunosuppressive effects of this class of drugs. Glucocorticoids: 
  • Oral or intramuscular
  • 1st-line therapy for stabilization of rapidly progressive disease
• Systemic immunosuppressants Immunosuppressants Immunosuppressants are a class of drugs widely used in the management of autoimmune conditions and organ transplant rejection. The general effect is dampening of the immune response. Immunosuppressants: 
  • Options: methotrexate Methotrexate An antineoplastic antimetabolite with immunosuppressant properties. It is an inhibitor of tetrahydrofolate dehydrogenase and prevents the formation of tetrahydrofolate, necessary for synthesis of thymidylate, an essential component of DNA. Antimetabolite Chemotherapy, mycophenolate Mycophenolate Immunosuppressants, cyclosporin
  • An alternative to systemic steroids Steroids A group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. Benign Liver Tumors

Other therapies

• Phototherapy Phototherapy Treatment of disease by exposure to light, especially by variously concentrated light rays or specific wavelengths. Hyperbilirubinemia of the Newborn:
  • Often used in conjunction with medical therapy
  • Used alone for stabilization of rapidly progressive disease if steroids Steroids A group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. Benign Liver Tumors are contraindicated
• Depigmentation therapy:
  • For extensive disease involving > 40% of body surface area
  • Used on areas of unaffected skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions
  • Goal is to match the diseased area for cosmetic satisfaction.
• Surgical transplantation procedures:
  • Techniques: skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions grafts, autologous melanocyte cultures
  • May be used for stable, localized lesions

Prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas

• Vitiligo is a chronic skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions condition.
• The clinical course is unpredictable.
• Lesions may stabilize or continue to progress and expand over the years, despite treatment.

Differential Diagnosis

• Nevus Nevus Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi depigmentosus: typically a benign Benign Fibroadenoma, solitary, localized hypopigmented macule Macule Nonpalpable lesion < 1 cm in diameter Generalized and Localized Rashes or patch Patch Nonpalpable lesion > 1 cm in diameter Generalized and Localized Rashes that is often noted at birth or in the early years of life. These lesions are stable and not progressive, although they may appear to enlarge as the body grows. Nevus Nevus Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi depigmentosus is caused by defective melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions that cannot produce pigment or transfer it to keratinocytes Keratinocytes Epidermal cells which synthesize keratin and undergo characteristic changes as they move upward from the basal layers of the epidermis to the cornified (horny) layer of the skin. Successive stages of differentiation of the keratinocytes forming the epidermal layers are basal cell, spinous or prickle cell, and the granular cell. Skin: Structure and Functions. Management is not necessary and, when attempted, has varied results.
• Pityriasis alba: a common skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions disorder typically affecting children and adolescents. The condition is often considered a manifestation of atopic dermatitis Dermatitis Any inflammation of the skin. Atopic Dermatitis (Eczema). Typically, patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship present with erythema Erythema Redness of the skin produced by congestion of the capillaries. This condition may result from a variety of disease processes. Chalazion and scale Scale Dermatologic Examination followed by round, hypopigmented macules and patches, which commonly occur on the face, upper trunk, or upper limbs. The diagnosis is clinical. Pityriasis alba is considered self-limiting Self-Limiting Meningitis in Children, but may take months to years to resolve. Topical steroids Steroids A group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. Benign Liver Tumors, emollients Emollients Oleaginous substances used topically to soothe, soften or protect skin or mucous membranes. They are used also as vehicles for other dermatologic agents. Pityriasis Rosea, and calcineurin inhibitors Calcineurin Inhibitors Compounds that inhibit or block the phosphatase activity of calcineurin. Immunosuppressants may be used to speed up resolution.
• Tinea (pityriasis) versicolor: a common superficial fungal infection caused by Malassezia Malassezia Malassezia is a lipophilic yeast commonly found on the skin surfaces of many animals, including humans. In the presence of certain environments or triggers, this fungus can cause pathologic diseases ranging from superficial skin conditions (tinea versicolor and dermatitis) to invasive disease (e.g., Malassezia folliculitis, catheter-associated fungemia, meningitis, and urinary tract infections). Malassezia Fungi furfur. Tinea versicolor Tinea versicolor A common chronic, noninflammatory and usually symptomless disorder, characterized by the occurrence of multiple macular patches of all sizes and shapes, and varying in pigmentation from fawn-colored to brown. It is seen most frequently in hot, humid, tropical regions and is mostly caused by Malassezia furfur (formerly Pityrosporum orbiculare). Malassezia Fungi may present as hypopigmented, hyperpigmented, or erythematous macules and patches, most often on the trunk. Diagnosis is often clinical but may be confirmed with visualization of hyphae Hyphae Microscopic threadlike filaments in fungi that are filled with a layer of protoplasm. Collectively, the hyphae make up the mycelium. Mycology and budding Budding Mycology cells on potassium Potassium An element in the alkali group of metals with an atomic symbol k, atomic number 19, and atomic weight 39. 10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the water-electrolyte balance. Hyperkalemia hydroxide wet mount. Management is with topical or oral antifungals.
• Halo nevus Nevus Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi: a mole Mole Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi surrounded by a halo of hypopigmentation Hypopigmentation A condition caused by a deficiency or a loss of melanin pigmentation in the epidermis, also known as hypomelanosis. Hypopigmentation can be localized or generalized, and may result from genetic defects, trauma, inflammation, or infections. Malassezia Fungi. Multiple lesions may be present, and the back is most often affected. Loss of pigment often precedes spontaneous resolution of the central nevus Nevus Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi. Repigmentation of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions may occur after the nevus Nevus Nevi (singular nevus), also known as “moles,” are benign neoplasms of the skin. Nevus is a non-specific medical term because it encompasses both congenital and acquired lesions, hyper- and hypopigmented lesions, and raised or flat lesions. Nevus/Nevi disappears. The diagnosis is generally clinical. No treatment is necessary.
• Chemical leukoderma: also known as occupational vitiligo, hypopigmentation Hypopigmentation A condition caused by a deficiency or a loss of melanin pigmentation in the epidermis, also known as hypomelanosis. Hypopigmentation can be localized or generalized, and may result from genetic defects, trauma, inflammation, or infections. Malassezia Fungi of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions resulting from contact with certain chemicals that cause melanocytotoxicity. Hypopigmentation Hypopigmentation A condition caused by a deficiency or a loss of melanin pigmentation in the epidermis, also known as hypomelanosis. Hypopigmentation can be localized or generalized, and may result from genetic defects, trauma, inflammation, or infections. Malassezia Fungi initially occurs in the area of contact but may spread to additional areas. The diagnosis is clinical. Management involves removal/avoidance of the offending agent and the use of topical steroids Steroids A group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons. Steroids have a common nucleus, a fused, reduced 17-carbon atom ring system, cyclopentanoperhydrophenanthrene. Most steroids also have two methyl groups and an aliphatic side-chain attached to the nucleus. Benign Liver Tumors.
• Idiopathic Idiopathic Dermatomyositis guttate hypomelanosis: benign Benign Fibroadenoma skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions condition that is thought to be a part of the natural aging process and is associated with a decrease in the number of melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions. Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship will have diffuse, small, round or oval hypopigmented macules on sun-exposed areas, most often on the extremities. Once present, these lesions are stable and do not change. The diagnosis is clinical. Treatment is not required.