Myxedema, strictly speaking, is a boggy swelling of the skin and subcutaneous tissue which results from the deposition of mucin. It traditionally occurs in hypothyroid states, and recognition of this generalized nonpitting edema provides the physician with a reason to suspect hypothyroidism.
The lesions of localized myxedema which usually occur in the pretibial areas are also collections of mucin in the skin, as the name implies. These circumscribed lesions develop not in the hypothyroid patient as one might expect, but rather in the hyperthyroid individual who almost invariably has exophthalmos. The lesions usually appear after medical or surgical suppression of thyroid activity.
Mucin in either type of myxedema appears to be the same. It represents an increase of the mucin normally present in the ground substance of the dermal connective tissue, and it can be demonstrated histochemically with a stain for acid mucopolysaccharides, such as Alcian blue, methylene blue, or