Common Skin Changes Associated with Thyroid Disease

Introduction:

Thyroid disorders are highly prevalent in medical practice and associated with a wide range of diseases with or without common etiological factors. One of the organs with a wide range of clinical signs associated with thyroid is the skin involving the three layers that are epidermis, dermis, and hypodermis, and the cutaneous phaneras - hair and nails.

In an attempt to simplify these skin manifestations, it is divided into two main groups:

• Skin lesions associated with thyroid diseases but with no cause-effect relationship.

• Skin lesions dependent on thyroid disease (hyper and hypothyroidism).

In most cases, the evolution and outcome of the skin lesions will depend on the thyroid function.

What Are the Skin Lesions Associated With Thyroid Disorders?

These cutaneous disorders are seen with greater incidence in patients affected by thyroid dysfunction than in the general population, though many of the symptoms may overlap with the thyroid disease itself. The most common association is pigmentation spots or dyschromia, which can be hyperpigmentation and hypopigmentation due to autoimmune disorders.

1. Hyperchromia includes melasma, and cafe-au-lait pigmentation, without itching or scaling. It is generally seen in dark-skinned women living in intense sunlight areas and is located in the center of the face. It is also proposed that sexual steroidal hormones (released during pregnancy or taken as oral contraceptives) trigger the development of melasma in women with predisposed thyroidal autoimmune diseases.

2. Hypochromia manifested as vitiligo is characterized by colorless patches with hyperpigmented margins. This lesion starts gradually without itch, numbness, scaling, atrophy, or sclerosis. They are symmetrical and present on the face, neck, back of the hands, folds, and genitals.

3. Dyschromia has increased frequency and severity in women.

4. Vogt-Koyanagi-Harada’s syndrome affects the tissues containing the melanin-producing cells and is associated with Hashimoto’s thyroiditis. Dermatitis herpetiformis is strongly associated with the atrophic variant of Hashimoto’s thyroiditis.

5. Alopecia areata is typically associated with thyroid diseases. Alopecia is circumscribed bald patches on the scalp or beard. The lesions appear clean with underlying hair follicles.

6. Patients with autoimmune thyroid diseases are associated with three variants of pemphigus: Vulgaris, erythematous, and foliaceous.

7. Chronic mucocutaneous candidiasis is characterized by chronic and recurrent fungal infections of the skin, nails, and oropharynx. Vertical transmission of chronic mucocutaneous candidiasis in families is associated with primary hypothyroidism.

8. Connective tissue diseases, like systemic lupus erythematosus (SLE), Scleroderma, and the CREST syndrome (Calcinosis, Raynaud’s phenomenon, Esophageal dysfunction, Scleroderma, Telangiectasias) display the strongest association with thyroid diseases.

What Skin Lesions Depend on Thyroid Disorders?

Hypothyroid State:

In hypothyroidism, the skin becomes dry, rough, and cool to the touch. Skin dryness is due to decreased sweating and sebum secretion, a condition known as hypohidrosis. As a reflex mechanism, the blood vessels in the skin constrict to maintain body temperature induced by hypothermia resulting in skin pallor and cool to touch. This is due to the metabolic changes by the thyroid hormones on the skin's blood flow.

All these disorders also develop friction-induced intra-epidermal bulla, purpura, and ecchymosis. The lack of metabolism of carotene (photosynthetic pigment) by the liver accumulates carotene in the skin layers. Carotene is then expelled out in the sweat and reabsorbed by the skin and deposited mainly in sebaceous gland-rich areas. This leads to a change in the skin color, giving a yellowish tint or carotenodermia.

Acquired variants of palmoplantar keratoderma with an increase in keratin production and reduced intercellular lipids, both contributing to changes in trans-epidermal water loss. When the skin thickening becomes generalized it is known as ichthyosiform or xeroderma, more often found in severe cases of hypothyroidism.

Pilose keratosis, characterized by dry scales, skin thickening, and keratosis of hair follicles with permanent hair loss is frequently associated with hypothyroidism. It is commonly seen in teenagers and is located in the back of arms and thighs.

Generalized myxedema or cutaneous mucinosis is characterized by diffuse swelling without depressions, noticeable in the periorbital and the extremities.

Mid-dermal elastolysis is the loss of elastic fibers in the dermis due to the engulfment of elastic fibers by the giant cells and granuloma formation is associated with Hashimoto’s thyroiditis.

Hypercholesterolemia, tuberous and eruptive xanthomas are also manifested in the skin of hypothyroid patients. The skin of these patients develops skin eruptions. Hair and nails are also affected by this systemic disorder. The decrease in oil production makes the hair opaque, retarded growth rate with delayed initiation of the hair growth. Hair loss causing diffuse alopecia is also possible. The nails become thin and brittle and grow slowly with longitudinal ridging. Also, onycholysis (the nail separated from the nail bed) and koilonychia (flat or concave nails) may develop.

Hyperthyroid State:

Hyperthyroid patients present increased activity and metabolism in the skin perfusion. Hence the skin is warm and moist to the touch, resulting in a condition known as hyperhidrosis. Erythema of the face and hands are also seen. Dermal vasodilation causes flushing as a regulatory mechanism for body temperature. The sebum excretion rate is normal.

Hyperpigmentation may be localized or diffuse.

Pretibial myxedema (severe hyperthyroidism) is most usually seen with Graves' disease. 3 % – 5 % of patients with Graves' disease develop myxedema, and 70 % – 90 % is associated with exophthalmos (bulging of eyes). When hyperthyroidism is combined with the bulging of both the eyes and the thickening of fingers and toes, it is known as diamond syndrome. Nails appear shiny and grow more rapidly. They may also be friable, and the lifting of the nail plate gives a ragged and dirty appearance known as Plummer’s nails. Beau’s ridge, a thick transverse ridge of nails, is commonly found.

Rarely, thyroid thickening may be seen which is characterized by a triad:

• Clubbing of the fingers or toes.

• Thickening and fibrosis of the subcutaneous tissue

• New bone formation in the extremities.

Thyroid Neoplasia:

Multiple endocrine neoplasias (MEN) are associated with medullary thyroid carcinoma, present as cafe-au-lait spots, diffuse hyper-pigmented spots, and nerve problems. Notalgia paresthetica is a benign skin disorder in the central upper back, seen as itchy bumps with skin pigmentation and amyloid deposit. Spreading of skin lesions from thyroid cancer is rare; however, patients with follicular and medullary variants of cancer are seen with isolated nodules in the head and neck.

Conclusion:

There are several skin disorders that are directly or indirectly associated with deviations in the thyroid level. In general, skin lesions associated with thyroid abnormalities mainly include autoimmune thyroid diseases and skin lesions depending on the thyroid disorder, in which the hormonal treatment leads to the cure or improvement of the skin lesion in most patients. The skin changes in hyper and hypothyroidism show a strong influence of the thyroid hormones on the skin tissue.