• Sketchy
• Osmosis
• Bootcamp
• Notes

• Small changes in thyroid hormone levels can lead to significant changes in serum TSH levels. In hypothyroidism, the TSH level rises before a low thyroid hormone level is detected, making serum TSH the most sensitive marker for diagnosing hypothyroidism.
• The serum TSH level is the single most important screening test for diagnosing primary hypothyroidism. Although TSH is not elevated in patients with central hypothyroidism, this condition is uncommon.
• In primary hypothyroidism, there is an increase in TSH and a decrease in free T4.
• In subclinical hypothyroidism, the TSH level is on the high side of normal, and the free T4 level is on the low side of normal.
• Increased TRH stimulates prolactin secretion, leading to hyperprolactinemia. In women, this may result in amenorrhea with galactorrhea or more often anovulatory cycles with menorrhagia. In men, it can cause infertility and gynecomastia.
• The accumulation of subcutaneous mucopolysaccharides can lead to a non-pitting edema (myxedema).
• Hypothyroidism can cause slow thinking and lethargy. Some patients may experience severe mental symptoms, dementia, or psychosis ("myxedema madness").
• Myxedema coma is the end stage of untreated hypothyroidism. Major features include hypoventilation, fluid and electrolyte imbalances, hypothermia, and ultimately shock and death.
• Involvement of the musculoskeletal system can cause hypothyroid myopathy, characterized by myalgia, proximal muscle weakness, and cramping.
• An increase in serum creatine kinase (CK), specifically the MM fraction, is common in hypothyroidism and can occur even in patients without symptoms.
• Muscle biopsy may reveal a variety of nonspecific changes. These include atrophy of type II fibers, hypertrophy of type I fibers, glycogen deposition, focal myonecrosis, and inflammatory infiltrates.
• In patients with unexplained CK elevation, hypothyroidism should be ruled out by measuring thyroid-stimulating hormone levels.
• Hypothyroidism should also be excluded in patients with unexplained hypercholesterolemia and unexplained menorrhagia.

Types of hypothyroidism.