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Patients with abnormal thyroid function of "new crown infection", why are other thyroid tests okay?

 Last Update: 2023-02-03
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Non-thyroid pathological syndrome, do you understand?

AuthorZhang Taisheng, Qionghai People's Hospital, Hainan Medical College

Under the ravages of the epidemic, many patients with fever have rushed into the hospital, especially some middle-aged and elderly patients
with underlying diseases.
In several patients recently consulted by the author, I found some interesting results of five tests of thyroid gong: Case a 47-year-old man, admitted to the hospital due to "repeated dry mouth, excessive drinking for more than 11 years, fever with shortness of breath for 2 days", the patient's diagnosis considered: adult occult autoimmune diabetes, diabetic ketoacidosis, fever investigation:
new coronavirus infection? Long-term four-dose insulin intensive blood sugar control before admission, after admission, due to five abnormalities of thyroid function, please consult with our department: case two, a 16-year-old woman, admitted to the hospital due to "polydipsia, polydipsia, weight loss for more than 4 years, fever with change in consciousness for 1 hour", considered for diagnosis: type 1 diabetes,

diabetic ketoacidosis; Fever investigation: novel coronavirus infection? After admission, please consult with our department due to abnormal thyroid function: case three, a 49-year-old man, was admitted to the hospital due to "dry mouth, polyuria for more than 3 years, nausea, vomiting with fever for 3 days", and considered for diagnosis: type 2 diabetes, nausea, vomiting Cause:
Diabetic ketoacidosis? Fever investigation: novel coronavirus infection? After admission, please consult with our department due to abnormal results of five thyroid grams: In response to these five results of thyroid function, the author asked these three patients one by one about the family history and symptoms of thyroid-related diseases, as well as relevant physical examinations of the thyroid gland, but without exception,

did not receive any affirmative answers and positive signs.
Even antibodies and thyroid ultrasound are negative
.

But the only similarity is that all 3 patients have different degrees of influence from acute complications of diabetes, and all patients have one trigger, that is, infection
.

There are many clinical diagnoses and treatments for hyperthyroidism and hypothyroidism, but some departments lack judgment and cognition of non-thyroid pathological syndromes, and at present, combined with the five results of these three cases, we will review this common disease
in the clinic again.

Definition and mechanism of occurrence

Non-thyroid disease syndrome (NTIS) refers to acute and chronic non-thyroid diseases in which thyroid hormone levels in the body drop below the normal reference value, and in addition to a decrease in T3 levels, normal or decreased T4 and TSH levels, and normal or elevated anti-T3 (rT3) levels, without the thyroid gland itself becoming diseased
。 It was previously thought to be a compensatory response to the body and normal thyroid function, hence the term normal thyroid pathological syndrome or low T3 syndrome
.
This condition is generally common in severe infections, trauma, burns, starvation, and even in patients with multiple organ dysfunction or injury
.

Diabetic ketoacidosis is more common
in people with diabetes hospitalized for acute complications.
And the change of thyroid hormone level is directly related
to the severity of the patient's hospitalization at that time.
The mechanism is as follows~

Changes in the hypothalamic-pituitary-thyroid axis

T3 is an activated form of thyroid hormone involved in the body's metabolism, and a decrease in serum T3 can reduce catabolism, reduce consumption, and prevent excessive metabolism
caused by thyroid in severe disease.
Therefore, hormonal changes are a mechanism
of self-protection for the body under the blow of severe disease or stress.
In this state, more cytokines act on the hypothalamic-pituitary-thyroid axis, affecting the regulatory mechanisms
such as thyroid hormone synthesis, regulation, and negative feedback.
It has become one of the main mechanisms of
systemic diseases leading to low T3 syndrome in the body.

Changes in the metabolism of thyroid hormones

80% of T4 is synthesized by 5-deiodinase in peripheral tissues such as liver and kidney, pituitary gland, and skeletal muscle, and converted into T3 or rT3, which become the main source of
T3 in the blood.
When the body suffers from greater trauma or stress, TT3 and FT3 in the body decrease, mainly due to multi-organ function damage, organ perfusion deficiency, liver and kidney failure and other factors, which can lead to the above synthesis process is limited, and the synthesis of hormones is reduced
.
Causes a decrease
in thyroid hormones.

Thyroid hormone and protein binding in the blood is restricted

When the body is in a state of long-term hunger, or severe malnutrition, nutrient absorption and utilization disorders
.
The patient's own protein is in a highly decomposed state, as the disease progresses, the protein becomes more and more deficient, the synthesis of thyroid-binding globulin decreases, the binding of T3 and T4 to globulin also decreases, and thyroid hormone synthesis can be limited, resulting in a decrease
in thyroid hormone synthesis.

Clinical signs

NTIS often has no special clinical symptoms, and the onset of patients is mainly primary severe disease
.
The vast majority of patients have no family history or symptoms
of thyroid-related disease.
However, due to the existence of different hormonal manifestation changes in NTIS, it is still necessary to be vigilant
in the history and hormone differentiation.

Clinically, primary hyperthyroidism and hypothyroidism are more common, and occasionally secondary hypothyroidism
is seen.
Thyrotoxicosis due to hyperthyroidism is due to oversynthesis and secretion of thyroid hormones, and diffuse toxic goiter (Graves disease) is the most common cause
of hyperthyroidism.
Thyrotoxicosis caused by non-hyperthyroidism involves excessive thyroid hormone intake due to the destruction of the thyroid gland and the inability of the thyroid gland to synthesize
hormones.

Clinical hypothyroidism is more common in women, and the first three main causes are: autoimmune hypothyroidism, hyperthyroidism I¹³¹ surgery, and thyroid
surgery.
Accounts for 90%
of all causes.

Comparison with hormone levels in other common thyroid diseases is as follows:

in differential diagnosis, remove hormonal abnormalities, It is also necessary to further improve the patient's thyroid symptoms and physical examination, and if necessary, further thyroid ultrasound and thyroid antibody examination are required to further identify
.
Especially when
hormonal changes are not noticeable.

NTIS is roughly classified as follows:

Connection to diabetes or complications

The three patients in the cases all had underlying diabetes disease, and the onset was mostly based on infection as a trigger, which induced the onset of diabetic ketoacidosis, resulting in abnormal metabolism of thyroid
hormones.

Thyroid dysfunction often occurs in people with
diabetes.
It is long-term hyperglycemia and acid-base imbalance that reduces the activity of 5'-deiodinase, affects the conversion of TT4 to TT3 in tissues, and leads to a decrease
in TT3 formation.
At the same time, the decrease in 5'-deiodinase activity reduces rT3 degradation, resulting in increased rT3
.

At the same time, the presence of hyperglycotoxicity, abnormal renal function, and severe disorders of glucose and lipid metabolism can lead to disorders of thyroid hormone synthesis; Secondly, in people who have been in a high glucose state for a long time, protein synthesis may be restricted, and thyroglobulin that can be bound is relatively reduced, which can lead to the appearance
of NTIS.

The degree to which serum TT3 and FT3 levels are reduced in patients with severe diabetes is related to the degree of disease, age, course, and glycaemic control, not the type of complications
.
It can play a protective role
in reducing energy consumption in the body.
Serum TT3, FT3 and TT4 and FT4 levels in NTIS patients have lower than normal thyroid function, and the more severe the degree of diabetic ketoacidosis, the higher the case fatality rate, and the lower
the serum T3 and T4 levels.

Patients with NTIS such as diabetes mellitus and low T3 syndrome should actively control blood glucose and eliminate acute complications such as ketosis, and thyroid hormone therapy
is not advocated.

Connection to infection

Due to the increase in the release of cytokines by infection, a large number of inflammatory factors reduce the synthesis of T3 and reduce the concentration
of T3 in the blood by inhibiting the production of TSH and regulating it through negative feedback.
And the degree of infection is directly related to the level of thyroid hormone, when the infection is more severe, the lower the thyroid hormone, indicating that the condition is more and more serious, and the prognosis is poor; The reverse is true
.

treat

The above abnormalities in thyroid hormones are more a self-protection mechanism for the body, reducing the calories consumed in the body and reducing the consumption
of nutrients.

Whether thyroid hormones in this disease are physiologic or pathological, and whether exogenous thyroid hormone supplementation is still controversial, most agree that the treatment of the primary disease should be the main treatment, and exogenous thyroid hormone supplementation is not required, because NTIS can be considered an adaptive mechanism to resist excessive catabolism and support the immune response in the acute phase, and NTIS will also improve as the primary disease
。
Although some literature studies suggest that T3 supplementation can reduce peripheral vascular resistance and improve cardiac output, there is no significant improvement
in improving cardiac load, reducing arrhythmias, and reducing ICU length of stay.

At present, there is still some controversy about the treatment of this program, so it is still advocated to treat the primary disease
.

References:

Research Progress on Normal Thyroid Dysfunction Syndrome (2020), Wang Feng, Yan Zongxun, China Medical Guide, Vol.
22, No.
8 (No.
202), 2020[2].
Research Progress on Normal Thyroid Dysfunction Morbid Syndrome (2019), Qin Yuan, Yang Ying, Journal of Kunming Medical University 2019,40(9):125~129
Chinese Medical Association, Guidelines for Primary Diagnosis and Treatment of Hyperthyroidism (2019 Edition), Chinese Journal of General Practitioners, 2019, 18(12): 1118-1128[4].
Chinese Medical Association, Guidelines for Primary Diagnosis and Treatment of Hypothyroidism (2019 Edition), Chinese Journal of General Practitioners, 2019, 18(11): 1022-1028[5].
Luo Jie, Wang Deming, Effect of non-thyroid disease syndrome on critically ill patients, Chinese Practical Medicine,[6].
Zheng Rendong, Re-understanding the pathogenesis of non-thyroid disease syndrome, Jiangsu Medical Journal, 0523-3685(2016)10-1165-03[7].
Liu Tao, Research progress of non-thyroid disease syndrome, Chinese Journal of Clinicians, DOI: 10.
3877/ cma．j.
issn．1674-0785．2013．08．056

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