Schilddrüsenhormontherapie

Zusammenfassung

Die primäre Hypothyreose, insbesondere die subklinische Hypothyreose infolge einer Autoimmunthyreoiditis ist die häufigste endokrine Erkrankung. Obgleich die Diagnose relativ einfach ist, wird die Frage ab wann eine L-Thyroxin-Substitution notwendig ist, kontrovers diskutiert. Bei manifester Hypothyreose, definiert als eine erhöhtes TSH und erniedrigtes FT4 oder ein TSH > 10 mU/L ist die Indikation zur Substitution eindeutig gegeben. Bei subklinischer Hypothyreose, definiert als erhöhtes basales TSH im Graubereich von 4–10 mU/L und noch normalem freien Thyroxin hängt die Indikation der Hormonsubstitution von der Grunderkrankung und den Begleitsymptomen ab. Das L-Thyroxin ist ein stoffwechselinaktives Prohormon und wird in den einzelnen Organen zum stoffwechselaktiven Trijodthyronin umgewandelt. Daher wird L-Thyroxin bevorzugt zur Substitution eingesetzt. Einige Patienten fühlen sich aber unter dieser Monotherapie nicht wohl, und in einigen Studien konnte gezeigt werden, das eine Kombinationstherapie von einigen Patienten besser vertragen wird. Dies konnte mit Polymorphismen der Typ-2 Dejodinase und damit geringerer intrazellulärer Trijodthyronin Bildung in Verbindung gebracht werden.

Zu beachten ist, dass insbesondere der Frühschwangerschaft der Bedarf an L-Thyroxin um 25–50 µg erhöht werden muss. Ferner hängt die Resorption von L-Thyroxin von einem normalen Magensäuregehalt ab, weswegen es nüchtern eingenommen werden muss, und Säureblocker, eine atrophischer Gastritis aber auch andere Substanzen die L-Thyroxin Aufnahme vermindern kann. Nur bei Patienten nach Thyreoidektomie wegen eines differenzierten Schilddrüsenkarzinomes mit höherem Malignitätsgrad ist eine TSH-suppressive Therapie notwendig, nicht bei okkultem papillärem Mikrokarzinom.

Abstract

The autoimmune thyroiditis with overt or subclinical primary hypothyroidism is the most common endocrine disease. Although the diagnosis of hypothyroidism is not difficult, the question when a replacement therapy in subclinical hypothyroidism should be initiated is still under discussion. In patients with overt hypothyroidism defined as low FT4 and elevated TSH or TSH > 10 mU/L a replacement with levothyroxine is clearly indicated. In patients with subclinical hypothyroidism defined as a TSH between 4 and 10 mU/L and normal FT4, the treatment with Levothyroxine depends on the underlying disease and symptoms. Levothyroxine is a prohormone with is activated by deiodination in the organs to triiodothyronine. Therefore, levothyroxine for replacement therapy is mainly used. Some patients, however, do not feel well with this treatment and therefore studies with a combination therapy of levothyroxine and triiodothyronine had been performed and it could be shown that this might be related to a polymorphism in type 2 deiodinase in some patients, with the consequence of lower intracellular triodothyronine formation.

In women on levothyroxine replacement therapy getting pregnant, the demand of levothyroxine increases up to 25–50 µg, especially in the early weeks of pregnancy. It also has to be considered that the resorption of levothyroxine depends on normal stomach acid and therefore patients on acid blockers or atrophic gastritis require higher dosages of levothyroxine.

Only patients after thyroidectomy because of differentiated thyroid carcinoma with higher grad of malignancy need a TSH suppressive therapy, those with occult papillary thyroid carcinoma the TSH should be within the low normal range.

Schlüsselwörter

L-Thyroxin - Hypothyreose - Autoimmunthyreoiditis

Keywords

L-thyroxine - hypothyroidism - autoimmunethyroiditis

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