Abstract
The diagnosis of central hypothyroidism is often suspected in patients with hypothalamic/pituitary pathology, in the setting of low, normal, or even slightly elevated serum TSH and low free thyroxine (FT4). We present four cases of central hypothyroidism (three had known pituitary pathology) in whom central hypothyroidism was diagnosed after the serum free thyroxine index (FTI) was found to be low. All had normal range serum TSH and free thyroxine levels. This report illustrates that the assessment of the serum FTI may be helpful in making the diagnosis of central hypothyroidism in the appropriate clinical setting and when free T4 is in the low-normal range, particularly in patients with multiple anterior pituitary hormone deficiencies and/or with symptoms suggestive of hypothyroidism.
Highlights
Central hypothyroidism is a rare cause of hypothyroidism in the general population, estimated to occur in 1 : 20,000 to 1 : 80,000 [1]
The diagnosis of central hypothyroidism is often suspected in patients with hypothalamic/pituitary pathology, in the setting of low, normal, or even slightly elevated serum TSH and low free thyroxine (FT4)
We present four cases of central hypothyroidism in whom central hypothyroidism was diagnosed after the serum free thyroxine index (FTI) was found to be low
Summary
Central hypothyroidism is a rare cause of hypothyroidism in the general population, estimated to occur in 1 : 20,000 to 1 : 80,000 [1]. The diagnosis of central hypothyroidism is often suspected in patients with hypothalamic/pituitary pathology, in the setting of low free thyroxine (FT4). In cases of central hypothyroidism, serum TSH can be low, within the normal reference range, or even slightly elevated since TSH may have reduced biologic activity but normal immunoactivity [2,3,4]. In cases where FT4 is frankly low, making the diagnosis of central hypothyroidism is usually straightforward. In cases where free T4 is within the normal reference range, especially in the setting of normal serum TSH, making the diagnosis of central hypothyroidism can be challenging. We present four cases of central hypothyroidism that were diagnosed via the assessment of serum FTI, in cases where patients had serum TSH and FT4 values within their respective reference ranges
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