MYXEDEMA
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.
