Latent Hypothyroidism: Complications

The following are the major conditions or complications that may be contributed to by latent (subclinical) hypothyroidism (hypothyroidism):

Certain conditions originating in the perinatal period (P00-P96).

  • Neurologic damage in the fetus

Endocrine, nutritional, and metabolic diseases (E00-E99).

  • Diabetes mellitus type 2
  • Increase of the homocysteine level
  • Hypercholesterolemia (increased levels of cholesterol in the blood; LDL cholesterol).
  • Hyperprolactinemia and male libido disorders – latent hypothyroidism leads to increased serum prolactin levels in men, which can be the cause of libido disorder.
  • Hyperprolactinemia and cycle disorders (oligomenorrhea/regular menstruation disorder: the interval between bleeding is > 35 days and ≤ 90 days to amenorrhea/> 90 days) – latent hypothyroidism usually leads to increased prolactin serum level in women, which can lead to follicle maturation disorders (egg maturation disorders) to anovulation (absence of the period) with prolonged cycles. This is usually accompanied by disruption of the second cycle phase (corpus luteum insufficiency) – as a result, fertility problems may occur.
  • Hyperuricemia (increase in uric acid levels in the blood) without signs of inflammatory arthritis (inflammation of the bones) or tophic gout
  • Manifest hypothyroidism (clinically striking hypothyroidism) – transition from latent to manifest hypothyroidism has been observed in 5% of patients/year
  • Nephropathy (kidney disease) in type 2 diabetics (type 2 diabetes mellitus).

Cardiovascular system (I00-I99)

  • Atherosclerosis (arteriosclerosis) – in women: with the consequence such as myocardial infarction (heart attack) or apoplexy (stroke).
  • Increased cardiac mortality (increased heart-related mortality).
  • Hypertension
  • Coronary artery disease (CAD; disease of the coronary arteries).
    • Esp. in patients with moderate to high Framingham risk score.
    • When the TSH level is above 10 mIE/l
  • Sudden cardiac death (PHT)

Musculoskeletal system and connective tissue (M00-M99).

Neoplasms – tumor diseases (C00-D48).

Psyche – Nervous System (F00-F99; G00-G99).

  • Male libido disorder
  • Neuromuscular weakness – weakness due to disorders of the nerves and/or muscles.
  • Psychiatric disorders such as depression

Pregnancy, childbirth and puerperium (O00-O99)

  • Abortion (miscarriage)

Symptoms and abnormal clinical and laboratory findings not elsewhere classified (R00-R99)

  • Bradycardia (<60 beats/minute).
  • Hypothermia – axillary basal temperature early in the morning in bed should ideally be at 36.4-36.8 ºC
  • Constipation (constipation)
  • Edema
  • Growth disturbance in the child

Genitourinary system (kidneys, urinary tract – sex organs) (N00-N99)

  • Female fertility disorder (due tohyperprolactinemia → corpus luteum insufficiency/yellow body weakness).

Further

  • Impairment of the heart:
    • Myocardial contractility (↓).
    • Diastolic function at rest ↓
    • Lack of adaptation of systolic function under physical exertion → limited exercise tolerance.
  • Increased mortality/sterility rate
    • TSH level ˃ 5.6 mlU/L and a free thyroxine [fT4] of 0.6-1.6 ng/dl (1.9-fold risk of mortality)
    • Hazard ratio for death in the elderly (mean: 83 years) with latent hypothyroidism: 1.75; 95% confidence interval: 1.63-1.88; follow-up: 10 years
    • In latent hypothyroidism (when TSH levels are above 10 mIE/l) due to ischemic heart disease or death from heart disease.
  • Disruption of endothelial function and limitation of heart rate variability.
  • Increased insulin sensitivity (in diabetics, this decreases daily insulin requirements!).

Prognostic factors

  • In patients on hemodialysis, hypothyroidism, as well as TSH levels in the upper normal range, is associated with increased mortality (death rate) (HR 1.47, 95% confidence interval 1.34-1.61; p < 0.001).