Symptoms of toxic multinodular goitre are similar to that of hyperthyroidism, including:

- heat intolerance

- muscle weakness/wasting

- hyperactivity

- fatigue

- tremor

- irritability

- weight loss

- osteoporosis

- increased appetite

- non-painful goitre (swelling of the thyroid gland)

- tachycardia (high heart rate - above 100 beats per minute at rest in adults)

Symptoms of the condition vary with type: hypo- vs. hyperthyroidism, which are further described below.

Possible symptoms of hypothyroidism are:

Possible symptoms of hyperthyroidism are:Note: certain symptoms and physical changes can be seen in both hypothyroidism and hyperthyroidism —fatigue, fine / thinning hair, menstrual cycle irregularities, muscle weakness / aches (myalgia), and different forms of myxedema.

Toxic multinodular goiter (also known as toxic nodular goiter, or Plummer's disease) is a multinodular goiter associated with hyperthyroidism.

It is a common cause of hyperthyroidism in which there is excess production of thyroid hormones from functionally autonomous thyroid nodules, which do not require stimulation from thyroid stimulating hormone (TSH).

Toxic multinodular goiter is the second most common cause of hyperthyroidism (after Graves' disease) in the developed world, whereas iodine deficiency is the most common cause of hypothyroidism in developing-world countries where the population is iodine-deficient. (Decreased iodine leads to decreased thyroid hormone.) However, iodine deficiency can cause goitre (thyroid enlargement); within a goitre, nodules can develop. Risk factors for toxic multinodular goiter include individuals over 60 years of age and being female.

Thyroid disease is a medical condition that affects the function of the thyroid gland (the endocrine organ found at the front of the neck that produces thyroid hormones). The symptoms of thyroid disease vary depending on the type. There are four general types: 1) hypothyroidism (low function) caused by not having enough thyroid hormones; 2) hyperthyroidism (high function) caused by having too much thyroid hormones; 3) structural abnormalities, most commonly an enlargement of the thyroid gland; and 4) tumors which can be benign or cancerous. It is also possible to have abnormal thyroid function tests without any clinical symptoms. Common hypothyroid symptoms include fatigue, low energy, weight gain, inability to tolerate the cold, slow heart rate, dry skin and constipation. Common hyperthyroid symptoms include irritability, weight loss, fast heartbeat, heat intolerance, diarrhea, and enlargement of the thyroid. In both hypothyroidism and hyperthyroidism, there may be swelling of a part of the neck, which is also known as goiter.

Diagnosis can often be made through laboratory tests. The first is thyroid-stimulating hormone (TSH), which is generally below normal in hyperthyroidism and above normal in hypothyroidism. The other useful laboratory test is non-protein-bound thyroxine or free T4. Total and free triiodothyronine (T3) levels are less commonly used. Anti-thyroid autoantibodies can also be used, where elevated anti-thyroglobulin and anti-thyroid peroxidase antibodies are commonly found in hypothyroidism from Hashimoto's thyroiditis and TSH-receptor antibodies are found in hyperthyroidism caused by Graves' disease. Procedures such as ultrasound, biopsy and a radioiodine scanning and uptake study may also be used to help with the diagnosis.

Treatment of thyroid disease varies based on the disorder. Levothyroxine is the mainstay of treatment for people with hypothyroidism, while people with hyperthyroidism caused by Graves' disease can be managed with iodine therapy, antithyroid medication, or surgical removal of the thyroid gland. Thyroid surgery may also be performed to remove a thyroid nodule or lobe for biopsy, or if there is a goiter that is unsightly or obstructs nearby structures.

Hypothyroidism affects 3-10% percent of adults, with a higher incidence in women and the elderly. An estimated one-third of the world's population currently lives in areas of low dietary iodine levels, making iodine-deficiency the most common cause of hypothyroidism and endemic goiter. In regions of severe iodine deficiency, the prevalence of goiter is as high as 80%. In areas where iodine-deficiency is not found, the most common type of hypothyroidism is an autoimmune subtype called Hashimoto's thyroiditis, with a prevalence of 1-2%. As for hyperthyroidism, Graves' disease, another autoimmune condition, is the most common type with a prevalence of 0.5% in males and 3% in females. Although thyroid nodules are common, thyroid cancer is rare. Thyroid cancer accounts for less than 1% of all cancer in the UK, though it is the most common endocrine tumor and makes up greater than 90% of all cancers of the endocrine glands.

Often these abnormal growths of thyroid tissue are located at the edge of the thyroid gland and can be felt as a lump in the throat. When they are large, they can sometimes be seen as a lump in the front of the neck.

Sometimes a thyroid nodule presents as a fluid-filled cavity called a thyroid cyst. Often, solid components are mixed with the fluid. Thyroid cysts most commonly result from degenerating thyroid adenomas, which are benign, but they occasionally contain malignant solid components.

The syndrome can present with variable symptoms, even between members of the same family harboring the same mutation. Typically most or all tissues are resistant to thyroid hormone, so despite raised measures of serum thyroid hormone the individual may appear euthyroid (have no symptoms of over- or underactivity of the thyroid gland). The most common symptoms are goiter and tachycardia. It has also been linked to some cases of attention deficit hyperactivity disorder (ADHD), although the majority of people with that diagnosis have no thyroid problems.

An association with depression has been proposed.

A goitre, associated with hypothyroidism or hyperthyroidism, may be present with symptoms of the underlying disorder. For hyperthyroidism, the most common symptoms are associated with adrenergic stimulation: tachycardia, palpitations, nervousness, tremor, increased blood pressure and heat intolerance. Clinical manifestations are often related to hypermetabolism, (increased metabolism), excessive thyroid hormone, an increase in oxygen consumption, metabolic changes in protein metabolism, immunologic stimulation of diffuse goitre, and ocular changes (exophthalmos). Hypothyroid individuals may have weight gain despite poor appetite, cold intolerance, constipation and lethargy. However, these symptoms are often non-specific and make diagnosis difficult.

Hyperthyroidism may be asymptomatic or present with significant symptoms. Some of the symptoms of hyperthyroidism include nervousness, irritability, increased perspiration, heart racing, hand tremors, anxiety, difficulty sleeping, thinning of the skin, fine brittle hair, and muscular weakness—especially in the upper arms and thighs. More frequent bowel movements may occur, and diarrhea is common. Weight loss, sometimes significant, may occur despite a good appetite (though 10% of people with a hyperactive thyroid experience weight gain), vomiting may occur, and, for women, menstrual flow may lighten and menstrual periods may occur less often, or with longer cycles than usual.

Thyroid hormone is critical to normal function of cells. In excess, it both overstimulates metabolism and exacerbates the effect of the sympathetic nervous system, causing "speeding up" of various body systems and symptoms resembling an overdose of epinephrine (adrenaline). These include fast heart beat and symptoms of palpitations, nervous system tremor such as of the hands and anxiety symptoms, digestive system hypermotility, unintended weight loss, and (in "lipid panel" blood tests) a lower and sometimes unusually low serum cholesterol.

Major clinical signs include weight loss (often accompanied by an increased appetite), anxiety, heat intolerance, hair loss (especially of the outer third of the eyebrows), muscle aches, weakness, fatigue, hyperactivity, irritability, high blood sugar, excessive urination, excessive thirst, delirium, tremor, pretibial myxedema (in Graves' disease), emotional lability, and sweating. Panic attacks, inability to concentrate, and memory problems may also occur. Psychosis and paranoia, common during thyroid storm, are rare with milder hyperthyroidism. Many persons will experience complete remission of symptoms 1 to 2 months after a euthyroid state is obtained, with a marked reduction in anxiety, sense of exhaustion, irritability, and depression. Some individuals may have an increased rate of anxiety or persistence of affective and cognitive symptoms for several months to up to 10 years after a euthyroid state is established. In addition, those with hyperthyroidism may present with a variety of physical symptoms such as palpitations and abnormal heart rhythms (the notable ones being atrial fibrillation), shortness of breath (dyspnea), loss of libido, amenorrhea, nausea, vomiting, diarrhea, gynecomastia and feminization. Long term untreated hyperthyroidism can lead to osteoporosis. These classical symptoms may not be present often in the elderly.

Neurological manifestations can include tremors, chorea, myopathy, and in some susceptible individuals (in particular of Asian descent) periodic paralysis. An association between thyroid disease and myasthenia gravis has been recognized. The thyroid disease, in this condition, is autoimmune in nature and approximately 5% of patients with myasthenia gravis also have hyperthyroidism. Myasthenia gravis rarely improves after thyroid treatment and the relationship between the two entities is not well understood.

In Graves' disease, ophthalmopathy may cause the eyes to look enlarged because the eye muscles swell and push the eye forward. Sometimes, one or both eyes may bulge. Some have swelling of the front of the neck from an enlarged thyroid gland (a goiter).

Minor ocular (eye) signs, which may be present in any type of hyperthyroidism, are eyelid retraction ("stare"), extraocular muscle weakness, and lid-lag. In hyperthyroid "stare" (Dalrymple sign) the eyelids are retracted upward more than normal (the normal position is at the superior corneoscleral limbus, where the "white" of the eye begins at the upper border of the iris). Extraocular muscle weakness may present with double vision. In lid-lag (von Graefe's sign), when the patient tracks an object downward with their eyes, the eyelid fails to follow the downward moving iris, and the same type of upper globe exposure which is seen with lid retraction occurs, temporarily. These signs disappear with treatment of the hyperthyroidism.

Neither of these ocular signs should be confused with exophthalmos (protrusion of the eyeball), which occurs specifically and uniquely in hyperthyroidism caused by Graves' disease (note that not all exophthalmos is caused by Graves' disease, but when present with hyperthyroidism is diagnostic of Graves' disease). This forward protrusion of the eyes is due to immune-mediated inflammation in the retro-orbital (eye socket) fat. Exophthalmos, when present, may exacerbate hyperthyroid lid-lag and stare.

Regarding morphology, goitres may be classified either as the growth pattern or as the size of the growth :

- Growth pattern:

- Uninodular goitre: one thyroid nodule; can be either an inactive or a toxic nodule.

- Multinodular goitre: multiple nodules; can likewise be inactive or toxic, the latter is called toxic multinodular goitre and associated with hyperthyroidism; thyroid cancer is identified in 13.7% of the patients operated for multinodular goitre. These nodules grow up at varying rates and secrete thyroid hormone autonomously, thereby suppressing TSH-dependent growth and function in the rest of gland.

- Diffuse goitre: the whole thyroid appearing to be enlarged due to hyperplasia.

- Size:

- Class I (palpation goitre): in normal posture of the head, it cannot be seen; it is only found by palpation.

- Class II: the goitre is palpable and can be easily seen.

- Class III: the goitre is very large and is retrosternal; pressure results in compression marks.

Thyroid storm is a severe form of thyrotoxicosis characterized by rapid and often irregular heart beat, high temperature, vomiting, diarrhea, and mental agitation. Symptoms may be unusual in the young, old, or pregnant. It is a medical emergency and requires hospital care to control the symptoms rapidly. Even with treatment, death occurs in 20% to 50%.

Thyroid nodules are nodules (raised areas of tissue or fluid) which commonly arise within an otherwise normal thyroid gland. They may be hyperplasia or a thyroid neoplasm, but only a small percentage of the latter are thyroid cancers. Small, asymptomatic nodules are common, and many people who have them are unaware of them. But nodules that grow larger or produce symptoms may eventually need medical care. Goitres may have nodules or be diffuse.

Almost all thyroid adenomas are follicular adenomas. Follicular adenomas can be described as "cold", "warm" or "hot" depending on their level of function. Histopathologically, follicular adenomas can be classified according to their cellular architecture and relative amounts of cellularity and colloid into the following types:

- Fetal (microfollicular) - these have the potential for microinvasion. These consist of small, closely packed follicles lined with epithelium.

- colloid (macrofollicular) - these do "not" have any potential for microinvasion

- embryonal (atypical) - have the potential for microinvasion.

- Hürthle cell adenoma (oxyphil or oncocytic tumor) - have the potential for microinvasion.

- Hyalinizing trabecular adenoma

Papillary adenomas are very rare.

A thyroid adenoma may be clinically silent ("cold" or "warm" adenoma), or it may be a functional tumor, producing excessive thyroid hormone ("hot" adenoma). In this case, it may result in symptomatic hyperthyroidism, and may be referred to as a toxic thyroid adenoma.

Hormone secreting pituitary adenomas cause one of several forms of hyperpituitarism. The specifics depend on the type of hormone. Some tumors secrete more than one hormone, the most common combination being GH and prolactin, which present as unexpected bone growth and unexpected lactation (in both men and women).

A patient with pituitary adenoma may present with visual field defects, classically bitemporal hemianopsia. It arises from the compression of the optic nerve by the tumor. The specific area of the visual pathway at which compression by these tumours occurs is at the optic chiasma.

The anatomy of this structure causes pressure on it to produce a defect in the temporal visual field on both sides, a condition called bitemporal hemianopsia. If originating superior to the optic chiasm, more commonly in a craniopharyngioma of the pituitary stalk, the visual field defect will first appear as bitemporal inferior quadrantanopia, if originating inferior to the optic chiasm the visual field defect will first appear as bitemporal superior quadrantanopia. Lateral expansion of a pituitary adenoma can also compress the abducens nerve, causing a lateral rectus palsy.

Also, a pituitary adenoma can cause symptoms of increased intracranial pressure.

Prolactinomas often start to give symptoms especially during pregnancy, when the hormone progesterone increases the tumor's growth rate.

Various types of headaches are common in patients with pituitary adenomas. The adenoma may be the prime causative factor behind the headache or may serve to exacerbate a headache caused by other factors. Amongst the types of headaches experienced are both chronic and episodic migraine, and more uncommonly various unilateral headaches; primary stabbing headache, short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) - another type of stabbing headache characterized by short stabs of pain -, cluster headache, and hemicrania continua (HS).

Non-secreting adenomas can go undetected for an extended time because no obvious abnormalities are seen; the gradual reduction in normal activities due to decreased production of hormones is rather less evident. For example, insufficient adrenocorticotropic hormone means that the adrenal glands will not produce sufficient cortisol, resulting in slow recovery from illness, inflammation and chronic fatigue; insufficient growth hormone in children and adolescents leads to diminished stature but which can have many other explanations.

Nontoxic nodular goiter is an enlarged thyroid without hyperthyroidism. It is often present for years before toxic nodular goiter occurs. In the United States it is the most common cause of a large thyroid affecting between 3 and 5% of the population.

The first signs of a parathyroid adenoma and the resulting primary hyperparathyroidism can include bone fractures and urinary calculi such as kidney stones.

Oftentimes parathyroid adenoma is not diagnosed until found on standard blood-tests that reveal high calcium content in the blood, it can appear in urine tests as well. Patients may not be experiencing any noticeable symptoms but could be producing excessive amounts of calcium and eventually experience problems later in life if untreated. However, patients can experience common symptoms that can range from joint, muscle, and abdominal pain to slight discomfort. Additionally patients might be experiencing feelings of depression due to the hormonal imbalance. Constipation and exhaustion can also be experienced as a result of the irregularity in the bloodstream. There is also a potential that the kidneys could be damaged with the excess of calcium in the blood.

Thyroid hormone resistance (sometimes Refetoff syndrome) describes a rare syndrome in which the thyroid hormone levels are elevated but the thyroid stimulating hormone (TSH) level is not suppressed, or not completely suppressed as would be expected. The first report of the condition appeared in 1967. Essentially this is decreased end organ responsiveness to thyroid hormones. A new term "impaired sensitivity to thyroid hormone" has been suggested in March 2014 by Refetoff et al.

Various psychiatric manifestations have been associated with pituitary disorders including pituitary adenomas. Psychiatric symptoms such as depression, anxiety apathy, emotional instability, easy irritability and hostility have been noted.

Symptoms caused by hormone excess and associated mass effects include:

The first step in diagnosing a thyroid neoplasm is a physical exam of the neck area. If any abnormalities exist, a doctor needs to be consulted. A family doctor may conduct blood tests, an ultrasound, and nuclear scan as steps to a diagnosis. The results from these tests are then read by an endocrinologist who will determine what problems the thyroid has.

Hyperthyroidism and hypothyroidism are two conditions that often arise from an abnormally functioning thyroid gland. These occur when the thyroid is producing too much or too little thyroid hormone respectively.

Thyroid nodules are a major presentation of thyroid neoplasms, and are diagnosed by ultrasound guided fine needle aspiration (USG/FNA) or frequently by thyroidectomy (surgical removal and subsequent histological examination). FNA is the most cost-effective and accurate method of obtaining a biopsy sample. As thyroid cancer can take up iodine, radioactive iodine is commonly used to treat thyroid carcinomas, followed by TSH suppression by high-dose thyroxine therapy.

Nodules are of particular concern when they are found in those under the age of 20. The presentation of benign nodules at this age is less likely, and thus the potential for malignancy is far greater.

Thyroid adenoma is a benign neoplasm of the thyroid. Thyroid nodules are very common and around 80 percent of adults will have at least one by the time they reach 70 years of age. Approximately 90 to 95 percent of all nodules are found to be benign.

Thyroid storm is characterized by an acute onset of symptoms of hyperthyroidism (fast heart rate, restlessness, agitation) accompanied by other features such as fever (temperatures often above 40 °C/104 °F), mental status changes, diarrhea, and vomiting.

Individuals can exhibit varying signs of organ dysfunction. Patients may experience liver dysfunction, and yellow discoloration of the skin is considered a poor prognostic sign. Heart (cardiac) symptoms include abnormal heart rhythms, decreased blood flow to the heart and heart attacks, and congestive heart failure, which may lead to cardiovascular collapse. Mortality can be as high as 20-30%.

In some situations, individuals may not experience the classic signs of restlessness and agitation, but instead present with apathetic signs of weakness and confusion.

Hyperpituitarism is a condition due to the primary hypersecretion of pituitary hormones, it typically results from a pituitary adenoma. Children with hyperpituitarism is rare, disruption of growth regulation, either because of hormone hypersecretion or because of manifestations caused by local compression of the adenoma can occur.

Signs and symptoms include: hypoglycemia, dehydration, weight loss, and disorientation. Additional signs and symptoms include weakness, tiredness, dizziness, low blood pressure that falls further when standing (orthostatic hypotension), cardiovascular collapse, muscle aches, nausea, vomiting, and diarrhea. These problems may develop gradually and insidiously. Addison's disease can present with tanning of the skin that may be patchy or even all over the body. Characteristic sites of tanning are skin creases (e.g. of the hands) and the inside of the cheek (buccal mucosa). Goitre and vitiligo may also be present. Eosinophilia may also occur.

There are three major types of adrenal insufficiency.

- Primary adrenal insufficiency is due to impairment of the adrenal glands.

- 80% are due to an autoimmune disease called Addison's disease or autoimmune adrenalitis.

- One subtype is called idiopathic, meaning of unknown cause.

- Other cases are due to congenital adrenal hyperplasia or an adenoma (tumor) of the adrenal gland.

- Secondary adrenal insufficiency is caused by impairment of the pituitary gland or hypothalamus. Its principal causes include pituitary adenoma (which can suppress production of adrenocorticotropic hormone (ACTH) and lead to adrenal deficiency unless the endogenous hormones are replaced); and Sheehan's syndrome, which is associated with impairment of only the pituitary gland.

- Tertiary adrenal insufficiency is due to hypothalamic disease and a decrease in the release of corticotropin releasing hormone (CRH). Causes can include brain tumors and sudden withdrawal from long-term exogenous steroid use (which is the most common cause overall).