The cutaneous changes observed in hypothyroidism belong to the most classic and frequent findings of the disease (Table 1). Although other important symptoms and signs of hypothyroidism may be present, changes in the skin may be the most important factor for seeking medical attention. In over 80% of patients with primary hypothyroidism, the epidermis is dry, rough, cool, and covered with fine superficial scales. This is an expression of decreased cutaneous metabolism, reduced secretion of sweat and sebaceous glands, vasoconstriction, thinning of the epidermis, and hyperkeratosis of the stratum corneum. The skin may have a finely wrinkled, parchment- like character. Unusual coldness of the arms and legs is sometimes a subject of complaint. The palms are cool and dry. Subcutaneous fat may be increased, with the formation of definite fat pads, especially above the clavicles, but is conspicuously absent in the more advanced form of the disease (myxoedematous cachexia). The hands and feet have a broad appearance, due to thickening of subcutaneous tissue.
Table1. Cutaneous signs and symptoms of hypothyroidism
The diffuse pallor and pale waxy surface colour can be attributed to two mechanisms. First vasoconstriction occurs and second the excess fluid and mucopolysaccharides in the dermis may compress small vessels to create blanching as well as interference with the transmission of colour from the deeper vessels. Anaemia may also contribute to pallor. Yellowish discolouration of the skin, most not ably of the palms, soles, and nasolabial folds, occurs in patients with long- standing hypothyroidism and is caused by elevation of serum and tissue carotene concentrations. The face is puffy, pale, and expressionless at rest. The skin of the face is also parchment- like. In spite of the swelling, it may be traced with fine wrinkles, particularly in pituitary myxoedema. The swelling sometimes gives it a round or moonlike appearance. The palpebral fissure maybe narrowed because of blepharoptosis, due to diminished tone of the sympathetic nervous fibres to Müller’s elevator palpebral superior muscle. The modest measurable exophthalmos seen in some patients with myxoedema is presumably related to accumulation of the same mucous oedema in the orbit as is seen elsewhere.
The tongue is usually large, and some patients will complain of this problem. The tongue is smooth if pernicious anaemia coexists. The voice is husky, low- pitched, and coarse due to the enlargement of the tongue and thickening of the pharyngeal and laryngeal mu cous membranes. The speech is deliberate and slow, and there may be difficulty in articulation.
There are other, less common, cutaneous findings seen in adult hypothyroid patients. Six patients have been reported in literature of an acquired palmoplantar keratoderma, verrucous in character, and predominantly affecting the plantar surface. An additional reported cutaneous finding specifically linked to atrophic thyroiditis is dermatitis herpetiformis, a gluten- sensitive skin disease characterized by blisters on the elbows, buttock, and knees.
Hair Follicles and Nails
The hair is dry, dull, and coarse, growing slowly, becoming sparse, and falling out readily. Loss of scalp, genital, and beard hair may also occur. Hair may be lost from the temporal aspects of the eye brows (Queen Anne’s sign). However, this sign is not uncommon in elderly euthyroid women and occurs in association with several types of cutaneous disease, including atopic dermatitis, seborrhoeic dermatitis, and lupus erythematosus. In men, the beard becomes sparse, and its rate of growth becomes greatly retarded. The scalp is dry and scaly. The nails, through retardation of growth, become thickened and brittle, striated both in transverse and longitudinal grooves, and show frequent deformities.
Dermal Changes
The dermal pathological findings in patients with hypothyroidism are clinically manifested by the non- pitting swelling, most marked around the eyes and hands, that is myxoedema. This is due to an ab normal accumulation of salts, mucopolysaccharides, and protein in the interstitial spaces of the skin. Histopathological examination of the skin reveals that the connective tissue fibres are separated by an increased amount of metachromatically staining, periodic acid- Schiff- positive mucinous material. This material consists of protein complexed with two mucopolysaccharides, hyaluronic acid and chondroitin sulphate B. An increase in the synthesis and accumulation of glycosaminoglycans leads to an excess of these normal intercellular substances.
The glycosaminoglycans are polymers of D- glucuronic acid and N- acetyl- D- glucosamine, forming hyaluronic acid, or of L- hyaluronic acid and N- acetyl- D- galactosamine sulphate, forming chondroitin sulphate B. They exist free and in ionic or covalent linkage to proteins. These mucoproteins comprise part of the normal non- fibrillar intercellular matrix, the ground substance holding cells together. Due to its strong water binding capacity, accumulated hyaluronic acid may also contribute to the peculiar non- pitting quality of myxoedema. Capillary permeability is augmented in hypothyroidism with increased accumulation of sodium, water, and proteins.
