Differentials
Primary hypothyroidism
SIGNS / SYMPTOMS
Absence of symptoms and signs of hypopituitarism such as central nervous system involvement (headaches, visual disturbances) or pituitary hormone excess (galactorrhoea, acromegaly, Cushing syndrome).
INVESTIGATIONS
Low serum free thyroxine is observed in both primary and central hypothyroidism.
A high thyroid-stimulating hormone (TSH) would be expected in primary hypothyroidism, whereas in central hypothyroidism TSH may be low, normal, or mildly elevated.
A high serum antithyroid peroxidase antibody concentration suggests primary hypothyroidism.
Non-thyroidal illness
SIGNS / SYMPTOMS
Abnormal findings on thyroid function tests that occur in the setting of a systemic non-thyroidal illness (NTI) without pre-existing hypothalamic/pituitary dysfunction.
The key characteristics are those of the primary disorder.
INVESTIGATIONS
The most prominent alteration is low serum triiodothyronine (T3).
Thyroid-stimulating hormone, total thyroxine (TT4), and free T4 (FT4) are also affected in variable degrees based on the severity and duration of the NTI.
As the severity of the NTI progresses, both serum T3 and T4 levels drop and then gradually normalise as the patient recovers.
Iodine deficiency
SIGNS / SYMPTOMS
Affected patients come from geographical regions where iodine deficiency disorders are endemic.
Individuals can present with goitre, short stature, and cognitive impairment.
INVESTIGATIONS
Occurs when dietary iodine intake is inadequate for thyroid hormone synthesis, resulting in primary hypothyroidism (elevated serum thyroid-stimulating hormone with low triiodothyronine [T3] and thyroxine [T4] levels).
Chronic fatigue syndrome
SIGNS / SYMPTOMS
Patients with both hypothyroidism and chronic fatigue syndrome may experience overlapping signs and symptoms, including prolonged fatigue as well as cognitive slowing and memory problems.
INVESTIGATIONS
Serum thyroid function tests are normal.
de Quervain's thyroiditis
SIGNS / SYMPTOMS
Symptoms of hypothyroidism may be present in the hypothyroid phase of de Quervain's thyroiditis, although most are transient. Local symptoms observed in de Quervain's thyroiditis, such as pain over the thyroid area, transient thyroid enlargement, and dysphagia, are not observed in central hypothyroidism.
INVESTIGATIONS
Serum thyroid-stimulating hormone is typically elevated in the hypothyroid period of de Quervain's thyroiditis.
In addition, serum thyroglobulin levels and erythrocyte sedimentation rate are almost always markedly elevated in de Quervain's thyroiditis, especially in the initial inflammatory/thyrotoxic phase.
Depression
SIGNS / SYMPTOMS
Slow mentation, fatigue, decreased memory, and somatic complaints are common in both depression and hypothyroidism.
Physical examination findings such as dry, coarse skin, periorbital puffiness, bradycardia, and delayed relaxation of deep tendon reflexes are not characteristic of depression.
Comorbid psychiatric disorders are more common in those with depression.
INVESTIGATIONS
Serum thyroid function tests are normal.
Eosinophilia-myalgia syndrome (EMS)
Fibromyalgia
SIGNS / SYMPTOMS
Symptoms common to central hypothyroidism and fibromyalgia include fatigue, depression, myalgias, and headaches (if central hypothyroidism is caused by a pituitary lesion).
A history of generalised pain with specific tender points suggests fibromyalgia.
INVESTIGATIONS
Serum thyroid function tests are normal.
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