Differentials
Central or secondary hypothyroidism
SIGNS / SYMPTOMS
Symptoms include those of primary hypothyroidism (fatigability, cold intolerance, weight gain) with or without other symptoms of hypopituitarism, including hypogonadism and secondary adrenal insufficiency.
Signs on physical examination indicate hypothyroidism, including skin changes, hair loss, and bradycardia. There may be other signs of a sellar or parasellar mass such as papilloedema and visual field deficits (a bitemporal hemianopsia).[31]
INVESTIGATIONS
Diagnostic evaluation of central hypothyroidism includes serum thyroid-stimulating hormone (TSH) and free thyroxine (T4). In central hypothyroidism, free T4 is low and TSH may be low, normal, or slightly elevated. MRI may reveal sellar or parasellar pathology.
Depression
SIGNS / SYMPTOMS
Many of the symptoms of hypothyroidism, which are non-specific, can be caused by depressive disorders. Both disorders are common in primary care practice. The symptoms of hypothyroidism respond to thyroid hormone replacement therapy; however, 5% to 10% of patients with well controlled levothyroxine-treated hypothyroidism have persistent symptoms.[1] Depressive disorders generally respond to treatment with antidepressants and/or behavioural therapy.
INVESTIGATIONS
Hypothyroidism is diagnosed by an elevated thyroid-stimulating hormone, which is normal in depression.
Alzheimer's dementia
SIGNS / SYMPTOMS
In older patients the two conditions may be indistinguishable. Cognitive dysfunction in hypothyroidism responds to thyroid replacement therapy.[1]
INVESTIGATIONS
Patients with Alzheimer's dementia have normal thyroid-stimulating hormone. Computed tomolography of the head may show signs of atrophy.
Anaemia
SIGNS / SYMPTOMS
Hypothyroidal and anaemic patients often have fatigue and dyspnoea on exertion. Primary hypothyroidism is associated with concurrent autoimmune conditions such as pernicious anaemia.[1]
INVESTIGATIONS
Thyroid-stimulating hormone (TSH) is elevated in primary hypothyroidism and the anaemia is usually normocytic. In other forms of anaemia, the TSH is not elevated and the red cells indices are variable (e.g., macrocytosis in pernicious anaemia, microcytosis in iron deficiency anaemia).
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