Early peripheral responses to intravenous L-thyroxine in primary hypothyroidism

Myxedema Coma: a Review

Myxedema coma, represents the extreme degree of severity of hypothyroidism, whose mortality can reach very high percentages, therefore, it is a true medical emergency. In general, its development is associated with the presence of a triggering factor in a controlled hypothyroid patient and manifests with multisystem alteration. Currently, tools have been developed for clinical diagnosis that use the profile and clinical models, and have good sensitivity-specificity. They allow an early diagnosis which favored the early start of treatment and therefore improves the prognosis. The patient with myxedema coma needs an integral approach, with intensive treatment and close monitoring of hemodynamic parameters. However, the basis of treatment remains hormone replacement, which should be initiated with a combination of levothyroxine and triiodothyronine.

Management of Endocrine Emergencies in the ICU

Endocrine emergencies are frequent in critically ill patients and may be the cause of admission or can be secondary to other critical illness. The ability to anticipate endocrine abnormalities such as adrenal excess or , hypothyroidism, can mitigate their duration and severity. Hyperglycemic crisis may trigger hospital and intensive care unit (ICU) admission and may be life threatening. Recognition and safe treatment of severe conditions such as acute adrenal insufficiency, thyroid crisis, and hypoglycemia and hyperglycemic crisis may be lifesaving. Electrolyte abnormalities such as hypercalcemia and hypocalcemia may have underlying endocrine causes, and may be treated differently with recognition of those disorders- electrolyte replacement alone may not be adequate for efficient resolution. Sodium disorders are common in the ICU and are generally related to altered water balance however may be related to pituitary abnormalities in selected patients, and recognition may improve treatment effectiveness and safety.

Intracerebral Bleeding and Massive Pericardial Effusion as Presenting Symptoms of Myxedema Crisis

The endocrinological emergency of a fully blown myxedema crisis can present as a multicolored clinical picture. This can obscure the underlying pathology and easily lead to mistakes in clinical diagnosis, work-up, and treatment. We present a case of an unconscious 39-year-old patient with a medical history of weakness, lethargy, and findings of hyponatremia, intracerebral bleeding, and massive pericardial effusion. Finally, myxedema crisis was diagnosed as underlying cause. Replacement therapy of thyroid hormone and conservative management of the intracerebral bleeding resulted in patient's survival without significant neurological impairment. However, diagnostic pericardiocentesis resulted in life-threatening pericardial tamponade. It is of tremendous importance to diagnose myxoedema crisis early to avoid adverse health outcomes.

Guidelines for the treatment of hypothyroidism: prepared by the american thyroid association task force on thyroid hormone replacement

BACKGROUND

A number of recent advances in our understanding of thyroid physiology may shed light on why some patients feel unwell while taking levothyroxine monotherapy. The purpose of this task force was to review the goals of levothyroxine therapy, the optimal prescription of conventional levothyroxine therapy, the sources of dissatisfaction with levothyroxine therapy, the evidence on treatment alternatives, and the relevant knowledge gaps. We wished to determine whether there are sufficient new data generated by well-designed studies to provide reason to pursue such therapies and change the current standard of care. This document is intended to inform clinical decision-making on thyroid hormone replacement therapy; it is not a replacement for individualized clinical judgment.

METHODS

Task force members identified 24 questions relevant to the treatment of hypothyroidism. The clinical literature relating to each question was then reviewed. Clinical reviews were supplemented, when relevant, with related mechanistic and bench research literature reviews, performed by our team of translational scientists. Ethics reviews were provided, when relevant, by a bioethicist. The responses to questions were formatted, when possible, in the form of a formal clinical recommendation statement. When responses were not suitable for a formal clinical recommendation, a summary response statement without a formal clinical recommendation was developed. For clinical recommendations, the supporting evidence was appraised, and the strength of each clinical recommendation was assessed, using the American College of Physicians system. The final document was organized so that each topic is introduced with a question, followed by a formal clinical recommendation. Stakeholder input was received at a national meeting, with some subsequent refinement of the clinical questions addressed in the document. Consensus was achieved for all recommendations by the task force.

RESULTS

We reviewed the following therapeutic categories: (i) levothyroxine therapy, (ii) non-levothyroxine-based thyroid hormone therapies, and (iii) use of thyroid hormone analogs. The second category included thyroid extracts, synthetic combination therapy, triiodothyronine therapy, and compounded thyroid hormones.

CONCLUSIONS

We concluded that levothyroxine should remain the standard of care for treating hypothyroidism. We found no consistently strong evidence for the superiority of alternative preparations (e.g., levothyroxine-liothyronine combination therapy, or thyroid extract therapy, or others) over monotherapy with levothyroxine, in improving health outcomes. Some examples of future research needs include the development of superior biomarkers of euthyroidism to supplement thyrotropin measurements, mechanistic research on serum triiodothyronine levels (including effects of age and disease status, relationship with tissue concentrations, as well as potential therapeutic targeting), and long-term outcome clinical trials testing combination therapy or thyroid extracts (including subgroup effects). Additional research is also needed to develop thyroid hormone analogs with a favorable benefit to risk profile.

Effect of short-term thyroxine administration on energy metabolism and mitochondrial efficiency in humans

The physiologic effects of triiodothyronine (T3) on metabolic rate are well-documented; however, the effects of thyroxine (T4) are less clear despite its wide-spread use to treat thyroid-related disorders and other non-thyroidal conditions. Here, we investigated the effects of acute (3-day) T4 supplementation on energy expenditure at rest and during incremental exercise. Furthermore, we used a combination of in situ and in vitro approaches to measure skeletal muscle metabolism before and after T4 treatment. Ten healthy, euthyroid males were given 200 µg T4 (levothyroxine) per day for 3 days. Energy expenditure was measured at rest and during exercise by indirect calorimetry, and skeletal muscle mitochondrial function was assessed by in situ ATP flux (³¹P MRS) and in vitro respiratory control ratio (RCR, state 3/state 4 rate of oxygen uptake using a Clark-type electrode) before and after acute T4 treatment. Thyroxine had a subtle effect on resting metabolic rate, increasing it by 4% (p = 0.059) without a change in resting ATP demand (i.e., ATP flux) of the vastus lateralis. Exercise efficiency did not change with T4 treatment. The maximal capacity to produce ATP (state 3 respiration) and the coupled state of the mitochondria (RCR) were reduced by approximately 30% with T4 (p = 0.057 and p = 0.04, respectively). Together, the results suggest that T4, although less metabolically active than T3, reduces skeletal muscle efficiency and modestly increases resting metabolism even after short-term supplementation. Our findings may be clinically relevant given the expanding application of T4 to treat non-thyroidal conditions such as obesity and weight loss.

Cardiogenic shock in a patient with hypothyroid myopathy responsive only to thyroxin replacement: a case report

The effect of hypothyroidism on the cardiovascular system has been well documented. Cardiac dysfunction due to hypothyroidism manifests as both systolic and diastolic dysfunction of the heart leading to cardiac arrhythmia and congestive heart failure. Its presentation in the form of refractory hypotension is rare. We describe a 52 year old man on whom Hypothyroid Cardiomyopathy manifested as cardiogenic shock responsive only to thyroxin replacement.

Appropriate replacement dose of thyroxine in primary hypothyroidism

An ultrasensitive thyrotropin (TSH) assay was used to determine how many of 65 patients with primary hypothyroidism on thyroxine (T4) replacement therapy had suppressed serum TSH. In 13 patients (20%) TSH levels less than or equal to 0.1 mIU/l were found, indicating an overdose of thyroxine. After correction of the dose, 48 patients had normal TSH values. Their mean dose of thyroxine was 119 micrograms/24 hours, and the appropriate replacement dose tended to decline with advancing age. The serum level of thyroid hormones during replacement therapy with thyroxine very imperfectly reflected serum TSH values. It is concluded that overdose of thyroxine is common when suppressed serum TSH is used as an end point. Biochemical follow-up of replacement therapy with thyroxine in primary hypothyroidism therefore requires the use of an ultrasensitive TSH assay in order to detect such suppression. Serum levels of thyroxine or triiodothyronine (T3) during thyroxine therapy are poor indicators of pituitary TSH secretion and are therefore not useful as parameters of adequate thyroxine dosage.

Perioperative management of patients with hypothyroidism

Hypothyroidism is a common disorder affecting the cardiovascular, respiratory, hematopoietic, and renal organ systems--each of which is particularly germane in the management of the surgical patient. In general, treatment of recognized hypothyroidism is recommended before any surgical procedure whenever possible and euthyroidism should be documented by measurement of serum TSH as part of the preoperative evaluation. Such a strategy is likely to result in better surgical outcomes with improved morbidity and mortality. One exception to treating first with thyroid hormone is the patient with angina or coronary artery disease requiring bypass grafting, angioplasty or stenting. In this setting, preoperative thyroid hormone therapy could tax the ischemic myocardium. The coronary blood flow should be addressed first, and thyroid hormone therapy initiated afterwards. The authors have emphasized the need for caution in the interpretation of low serum thyroid hormones in sick or surgical patients because of the importance of distinguishing between hypothyroidism and the "euthyroid sick syndrome." There is no clear evidence at this point to support thyroid hormone replacement in the latter patients, and it may be potentially harmful. Rather, we hold that T3 treatment of various surgical and other patients with nonthyroidal illness should be deferred until proof of its therapeutic efficacy is demonstrated.

Clinical, metabolic, and organ-specific indices of thyroid function

Presently there are a sufficient number of sensitive and specific tests of thyroid function to establish a diagnosis of thyroid disease with a high degree of precision. A variety of clinical situations, however, including but not limited to thyroid hormone resistance states, alterations in thyroid-binding proteins and nonthyroidal illness, challenge the clinician to evaluate the thyroid status of the patient beyond that which can be done with routine laboratory tests. This article reviews several clinical, cardiac, skeletal muscle, and other laboratory studies that have been suggested to complement the overall assessment of thyroid status.

Recognition and management of cardiovascular disease related to thyroid dysfunction

Hypothyroidism and hyperthyroidism are both associated with clinically significant cardiovascular derangements. In hypothyroidism, these include pericardial effusion, heart failure, and the complex interrelationship between hypothyroidism and ischemic heart disease. Cardiovascular disorders associated with hyperthyroidism include atrial tachyarrhythmias, mitral valve dysfunction, and heart failure. Although these usually occur in individuals with intrinsic heart disease, thyroid dysfunction alone rarely causes serious but reversible cardiovascular dysfunction. Patients with commonly encountered cardiac disorders, e.g., idiopathic cardiomyopathy and atrial fibrillation, should be screened for potentially contributing subclinical thyroid diseases. In patients with heart failure and hypothyroidism, initial management should focus on diagnosis and optimal management of any primary cardiac disease, whereas in hyperthyroidism, aggressive measures to control excess thyroid hormone action should generally have the highest priority.

Prediction and reversal of blunted ventilatory responsiveness in patients with hypothyroidism

To define the prevalence of impaired ventilatory responses in hypothyroidism, clinical and chemical parameters predicting their presence, and the potential for their acute reversal, ventilatory responses to hypercapnia and hypoxia were studied in 38 hypothyroid patients before treatment, and after short-term (seven days) and long-term (12 to 24 weeks) thyroid hormone therapy. Before treatment, hypercapnic ventilatory responses were blunted in 10 of 29 patients (34 percent), whereas hypoxic ventilatory responses were abnormal in eight of 30 patients (27 percent). Hypothyroid women and patients with marked pretreatment elevation of the serum thyrotropin concentration (greater than 90 mU/liter) were significantly more likely to have impaired ventilatory responses. In patients with an abnormal pretreatment response, parenteral thyroid hormone therapy (25 to 50 micrograms of L-triiodothyronine or 100 micrograms of L-thyroxine per day for seven days) significantly enhanced hypercapnic (0.75 +/- 0.06 to 1.19 +/- 0.16 liters/minute/mm Hg, p less than 0.05) and hypoxic (93 +/- 12 to 176 +/- 31 liters.mm Hg/minute, p less than 0.05) ventilatory responsiveness acutely. In seven of nine patients with abnormal pretreatment hypercapnic responses, and six of eight patients with abnormal hypoxic responses, normal ventilatory responsiveness was restored after one week of therapy. It is concluded that: (1) a subset of hypothyroid patients have blunted ventilatory responses to hypercapnia and/or hypoxia; (2) hypothyroid women and patients with a serum thyrotropin greater than 90 mU/liter more often manifest this abnormality; and (3) thyroid hormone therapy for one week reverses impaired ventilatory responses in hypothyroidism.

Hypothyroid cardiomyopathy: echocardiographic documentation of reversibility

The concept of hypothyroid heart disease remains controversial. Although hemodynamic abnormalities have been described, the presence of underlying abnormal cardiac structures has not been confirmed. The authors studied 20 hypothyroid patients using M-mode echocardiography before and after l-thyroxine therapy. Fifteen additional hypothyroid patients were studied using two-dimensional echocardiography to confirm the data of the first study. The findings were the same in both studies: during hypothyroidism, the interventricular septum is thickened, the ratio of septal thickness to left ventricular posterior wall thickening is increased, the right ventricular wall is thickened, regional wall motion of interventricular septum and right ventricular wall is decreased, and global function of the left ventricle is decreased. These findings are reversed with l-thyroxine therapy; they occur within 6 months of the development of hypothyroidism, but appear unrelated to elevated TSH levels. Whether the thickened interventricular septum and right ventricular wall represent true muscular hypertrophy requires further elucidation. Nevertheless, these data demonstrate the existence of a hypothyroid cardiomyopathy.

Adult hypothyroidism. 2. Causes, laboratory diagnosis, and treatment

Hypothyroidism may be self-limiting or may progress to thyroid failure, depending on the cause. Thus, diagnosis of the underlying disorder is extremely important. Once the diagnosis is established, the origin and cause of hypothyroidism must be identified. A careful history and physical examination, routine laboratory tests, and demonstration of antithyroid antibodies will ordinarily lead to the correct diagnosis. Self-limited disorders require little or no therapy. Progressive disease is treated with a thyroid hormone preparation. Myxedema coma is an endocrine emergency that requires prompt treatment of both the metabolic complications and any intercurrent illness.

Acute effect of exogenous thyroxine dose on serum thyroxine and thyrotrophin levels in treated hypothyroid patients

Acute effects of exogenous thyroxine on the serum thyroxine (T4), free thyroxine (FT4) and thyrotrophin (TSH) levels were studied in 20 hypothyroid women during the long-term maintenance therapy. All patients were euthyroid by clinical and laboratory parameters (T4). In nine patients TSH secretion was totally suppressed (less than 1 mu/l) by the mean dose of 178 micrograms thyroxine. Eleven patients had TSH values greater than 1 mu/l. Their mean thyroxine dose (132 micrograms) was not significantly lower than that which totally suppressed the TSH secretion. Ingestion of thyroxine resulted in maximal T4 and FT4 levels at 2 h after taking the drug. Simultaneously TSH concentration reached its minimum. The results indicate that it is necessary to know when the patient has taken the thyroxine in relation to determination of T4, FT4 and TSH levels in order to make the right decisions about the substitution dose of thyroxine. Thus it is essential to take blood sample for hormone determination before the patient ingests the daily thyroxine dose. However, among hypothyroid patients substituted by thyroxine there are individuals whose TSH secretion is not suppressed by normal T4 and FT4 levels.