Hypothyroidism slows many organ systems, and the picture it produces ranges from goiter alone to the full classical syndrome, depending on how long the hormone has been low and how far it has fallen.
Presentation in Hashimoto’s thyroiditis and atrophic thyroiditis
The clinical manifestations of Hashimoto’s thyroiditis vary between patients. Some have no manifestation of hypothyroidism at all and present with goiter (an enlarged thyroid gland) alone, which:
- is not very large
- has an irregular and firm consistency of the gland
- is rarely painful
By contrast, all patients with atrophic thyroiditis develop the classical signs and symptoms of hypothyroidism, because by then the gland has little working tissue left.
General features
The slowing of metabolism produces a set of symptoms that are easy to attribute to other causes: fatigue and lethargy, cold intolerance, constipation, dry skin, hoarseness, and slowed thinking. Weight rises despite a normal or reduced appetite, and, contrary to the popular idea, the increase is mainly due to retention of fluid rather than to higher food intake.
Cardiovascular changes
In the cardiovascular system, hypothyroidism causes reduced myocardial contractility and a reduced heart rate, which lowers cardiac output overall. Peripheral vasoconstriction, from lower production of NO (nitric oxide) by endothelial cells, leads to hypertension and peripheral cooling.
Fluid also accumulates in different parts of the body: most often as a pericardial effusion, in about 30% of cases, but also in the middle ear, leading to conductive deafness, and in the pleural space.
Neuromuscular and neurological findings
Slowing also reaches the muscles and nerves. Hypothyroidism can cause carpal tunnel syndrome, stiffness of muscle leading to cramps and muscle pain, and slow relaxation of the tendon reflexes.
In the brain, memory and concentration can be impaired. Glucose use by the brain can be reduced in the amygdala, the hippocampus and some other areas, as shown by PET (positron emission tomography) scanning, and this improves after treatment.
Hashimoto’s encephalopathy is a further neurological complication, which is steroid-responsive and associated with the TPO (thyroid peroxidase) antibody, myoclonus (sudden involuntary muscle jerks), and slow-wave electroencephalography.
Sexual and reproductive effects
Hypothyroidism affects sexual activity in both men and women, through:
- decreased libido
- oligomenorrhea (infrequent menstruation) and amenorrhea (absent menstruation)
- reduced fertility
- increased risk of miscarriage
The prolactin level is raised in some cases, which changes libido and fertility and can cause galactorrhea (inappropriate milk secretion), although this is unusual. The likely reason is a rise in TRH (thyrotropin-releasing hormone) production, since TRH stimulates prolactin production alongside TSH (thyroid-stimulating hormone) production.
Association with other autoimmune diseases
All the signs and symptoms above are produced by the low level of thyroid hormone. Beyond that, autoimmune disease of the thyroid gland is often accompanied by other autoimmune diseases, such as type 1 diabetes mellitus, SLE (systemic lupus erythematosus), Addison’s disease, arthritis, or vitiligo.
Because so many of these features are easy to attribute to other causes, the diagnosis rests on laboratory testing.