Myxedema is seen in patients with untreated severe hypothyroidism. This condition results from a total lack of thyroid hormone secretion and resultant deposition of mucopolysaccharides into the skin and other organs. Many skin and systemic findings are present in severe hypothyroidism. This is a condition seen in adults. The infantile form, called cretinism, is still found in parts of the world that do not routinely test newborn infants. If it is left untreated, mental retardation and various neurological deficits can occur. Adult myxedema is an uncommon clinical disease.
Clinical Findings: Patients usually develop severe hypothyroidism slowly. It can be caused by autoimmune thyroiditis, a thyroid tumor, a pituitary tumor or infarction, or hypothalamic disease. It can also be seen after treatment of hyperthyroidism with improper replacement of thyroid hormone. The onset of symptoms begins as mild, nondescript findings and advances to severe clinical disease as the lack of thyroid hormone worsens. Patients have many constitutional symptoms and always complain of fatigue, cold intolerance, and a generalized malaise. Constipation and weight gain are almost universal. Some patients develop a pericardial effusion and bradycardia. Neurological reflexes are blunted, and patients complain of slow mental reflexes.
The skin findings are specific to myxedema and can help one make the diagnosis. Patients develop diffuse, nonscarring alopecia. The hair is often dry and breaks easily. The lateral half of the eyebrows is shed. Finger- nails become brittle and lift off the nail bed. The facial features appear lethargic. Periorbital edema is prominent. Dry skin is severe and can mimic ichthyosis vulgaris. The skin on the lips is thickened, as is the tongue. The tongue may enlarge to the point that the impression of the teeth is seen on its lateral edges. If the infiltrate of mucopolysaccharides is extreme, the scalp can become thickened and furrowed, taking on the appearance of cutis verticis gyrate. The skin may acquire a subtle yellow hue due to carotinemia; this is most likely to be observed on the glabrous skin.
Laboratory findings are diagnostic and necessary. A nonspecific mild anemia is seen, consistent with anemia of chronic disease. Hypercholesterolemia and hyponatremia are two of the nonspecific findings. Electrocardiography shows bradycardia and a prolonged PR interval. The results of various thyroid hormone tests are characteristic. An elevated level of thyroid-stimulating hormone (TSH) is confirmatory for a diagnosis of primary hypothyroidism. Thyroxine (T4) levels are low and can be measured in various ways.
It is critical to differentiate adult generalized myxedema, as seen in hypothyroidism, from pretibial myxedema. Pretibial myxedema is a marker for hyperthyroidism, not hypothyroidism.
Pathogenesis: Thyroid hormone is required for multiple metabolic pathways to work properly, including the breakdown of glycosaminoglycans. When there is a decrease or a total lack of thyroid hormone, glycosaminoglycans cannot be properly metabolized, and they accumulate in the subcutaneous tissue, most prominently in the tissue of the face and scalp. This leads to the characteristic skin findings in myxedema.
Histology: Biopsy specimens of involved skin show mild deposition of mucin between collagen bundles within the dermis. Hyaluronic acid makes up the majority of the mucin deposits. The alopecia is nonscarring.
Treatment: Prompt recognition and diagnosis of myxedema is required. It is a fatal condition if left untreated, and myxedema coma is precipitated by a total lack of thyroid hormone. Thyroid replacement with levothyroxine (synthetic T4) is required.
Supportive care is necessary until the patient can be adequately stabilized. Determining the cause of the hypothyroidism is necessary to probe for thyroid cancer, pituitary problems, or other hypothalamic disease. Prompt recognition of the skin manifestations and referral to an endocrinologist can be life-saving. Once proper thyroid replacement has been achieved, the skin and hair findings slowly resolve over time.