Central hypothyroidism and subclinical hypo with normal thyroid panel

[pattismith]

Clinical and hormonal characteristics of central hypothyroidism at diagnosis and during follow-up in adult patients.
2004

Abstract
OBJECTIVE:
We studied the clinical and hormonal profiles of patients with central hypothyroidism (CH), the adequacy of levothyroxine (L-T4) treatment and the influence of other pituitary hormone replacement therapies.

METHODS:
We reviewed medical records of 108 adult patients with child-onset (CO; n=26) or adult-onset (AO; n=82) CH.

RESULTS:

At diagnosis, the most frequently reported symptoms were fatigue and headaches in AO patients, and growth retardation in CO patients.

Serum TSH was normal in a majority of CH patients, low in 8% and elevated in 8%.

Serum free thyroxine (fT(4)) was usually reduced, but remained within the low normal range in 28% of the study population (mostly CO patients).

Similarly, serum total T(4) (tT(4)), total triiodothyronine (tT(3)) and free T(3) (fT(3)) were found to be within the normal range in significant subsets of patients.

Interestingly, the clinical and biochemical characteristics of CH patients with normal f/t T(4) levels were not different from those of the patients with low fT(4) values.

The thyroid hormonal profile was not influenced by gender, etiology or by the number of hormone deficiencies.
At last evaluation, the mean dose of L-T(4) was 1.6+/-0.5 microg/kg/day and was negatively correlated to current age (P<0.001) but positively correlated to the number of hormone deficiencies (P<0.05).

Treatment suppressed TSH in 75% of the patients, induced normal fT(4) in 94%, but normal fT(3) in only 49% of them.

Male GH-treated patients and estrogen-treated females needed a higher L-T(4) dose compared with non-treated patients.

CONCLUSIONS:

fT(4) is clearly the best indicator of CH, but remains in the low normal range in a significant subset of patients, especially in those with CO disease.
Adequacy of therapy is mostly reflected by the combination of upper normal fT(4) and low normal fT(3) levels. Pituitary hormone replacement therapy may require an adjustment of T(4) treatment, as female patients under estrogen treatment and male patients under GH treatment will need a higher T(4) dose in order to remain in the euthyroid range.

 

[Nine lives]

Pre-onset back in 2002 I was once tested for thyroid (not taking thyroid medication):

TSH: 1.33 mU/l

FT4: 10.61 pmol/l (range 7.5 to 21.1)

FT3: 6.22 pmol/l (range 3.67 to 10.3)

This was deemed normal but it looks hypopituitary to me. SPINA results say:

Structural parameters:

GT: 2.47 pmol/s (thyroids max secretory capacity)

GD: 54.21* nmol/s (sum activity of peripheral 5'-deiodinases)

sGD: 4.84*

TSHI: 1.7

sTSHI: -1.46

TTSI: 78* (pituitary function)

 

[pattismith]

@Nine lives

it could be, because you have fT4 and TSH both in the lower third part of normal ranges.

fT3 is high which could indicate a high deiodination level (this correlates with high GD).
Do you have anti thyroglobulin antibodies?

although I have not read myself the full article quoted above, this paper concludes from it's analysis:


"Interestingly, time-related decreases in circulating FT4 concentrations larger than 20% vs. the initial FT4 determination were reported to support the diagnosis of CH in patients with different pituitary diseases followed for several years (61).
This cutoff value was set on the basis of a 10% variation over time of T4 levels in normal individuals (73). Provided that FT4 determination is repeatedly performed in the same laboratory, this approach would then allow the diagnosis and treatment of mild or hidden hypothyroid states of central origin.

The indexes of peripheral thyroid hormone action, such as SHBG, bone markers, serum lipids and others, lack sufficient sensitivity and specificity for the diagnosis of mild or subclinical hypothyroidism, especially in patients who present with CPHD, which may per se affect the levels of these indexes (60, 61, 74, 75).

Very recently, the determination of parameters of Doppler echocardiography including the isovolumic contraction time, isovolumic contraction time/ejection time, and myocardial performance index were, however, demonstrated to correlate with the presence of CH in a cohort of patients with hypothalamic-pituitary diseases, thus suggesting a potential use in the diagnosis of hidden CH (76).
Because abnormalities in cardiac parameters reverted during LT4 replacement, these findings may also indicate the requirement for LT4 treatment even in milder forms of the disease, as previously claimed in subclinical primary hypothyroidism (77)."

If Dr Luca Persani is right, it means that you have to repeat the fT4 test, and if you have a 20 % decrease over time, it is meaningful of a lack of fT4 production, with potential clinical effects. (do you have other fT4 tests you could compare?)

The other way you can detect a lack of thyroid hormon would be as suggested a Doppler echocardio, which seems to be the more sensitive test to do.

 

[Nine lives]

Thanks for finding this. I vaguely remember talking to my old hormone MD (before I moved) and we discussed central hypothyroidism. Now, I am on thyroid meds: a mix of T4 and desiccated (my old hormone MD firmly believed pig hormone ratios are not optimal for humans). I tried going all desiccated and SHBG climbed super high so in my case I think he was right.

Never had thyroid antibodies - tested a few times over last 8 years.

The only other (pre-thyroid medication) reading is in 2011 post floxing:

2011 Floxed

TSH: 1.27
FT4: 1.2 (0.82 - 1.77)
FT3: 2.1 (2 - 4.4)

This shows a big fT3 drop.

Structural parameters:
GT: 3.71 pmol/s
GD: 19.31* nmol/s
sGD: -2.14*
TSHI: 2.3
sTSHI: -0.57
TTSI: 109

Iodinisation messed up by fluoride perhaps?

 

[pattismith]

between the two tests, you still had a high pituitary sensitivity to TH (which can mean central hypothyroidism as well),
but a very different T3/T4 ratio that produces a low GD (bad deiodination).
This test would fit with a low T3 state or a low T3 syndrome at that time.

Low T3 syndrome can happen with many critical and chronic illnesses, so in your case, it can be a consequence of the illness that requiered a fluoroquinolone treatment.

I guess we can compare fT4 values only if the units are the same and if the test was done by the same lab.

Thanks for finding this. I vaguely remember talking to my old hormone MD (before I moved) and we discussed central hypothyroidism. Now, I am on thyroid meds: a mix of T4 and desiccated (my old hormone MD firmly believed pig hormone ratios are not optimal for humans). I tried going all desiccated and SHBG climbed super high so in my case I think he was right.

Did you feel better on thyroid meds?

Interestingly, my thyroid panel looked similar to your first one, (it was just before I started T3 supplementation), did you had a rT3 test?

TSH = 0.97 µUI/ml (0.4 - 4)
fT4 = 1.01 ng/dl (0.7 - 1.48 )
fT3 = 1.9 pg/ml (1.88 - 3.18)