Challenges in diagnosing central hypothyroidism

Öz

Purpose: A decline in serum free thyroxine (fT4), accompanied by an inadequate thyroid-stimulating-hormone (TSH) increase, indicates central hypothyroidism (CH) or non-thyroidal illness syndrome (NTIS). Distinguishing between two clinical circumstances is crucial due to variations in treatment approaches. In this study, we aimed to obtain clinical clues to distinguish between two conditions. Materials and methods: This retrospective study was conducted on 650 children and adolescents referred to the pediatric endocrine outpatient clinic due to low fT4 levels and TSH levels below 10 mIU/L. fT3, fT4, and TSH were measured at least 2 weeks apart for 3-times, and the patients with no fT4 increase in the third measurement were diagnosed with CH. Levothyroxine was started for patients with CH. After levothyroxine withdrawal, normal fT4 indicated transient CH; low fT4 indicated permanent CH. Factors affecting the development of permanent CH were investigated. Results: Fifty-three patients (25 females, 28 males) had low fT4 and a TSH level below 10 mIU/L by 6 weeks. The patients with permanent CH were found to have substantially lower fT4 and TSH levels, whereas fT3 was lower in the patients with transient CH (p<0.001, p=0.03, p=0.01, respectively). Lower fT4 was the only significant predictor that was independently associated with increased likelihood of permanent CH (OR:-0.52, 95% CI:0.3-0.9, p=0.014). Furthermore, the cut-off value for fT4 in the diagnosis of permanent CH was determined to be below 8.5 ng/L (Sensitivity: 75%, specificity: 71%). Conclusion: Likelihood of permanent CH is reduced in the patients with fT4 levels exceeding 8.5 ng/L. Prolonged follow-up would be a cost-effective measure in such patients, avoiding unnecessary laboratory investigations and therapeutic interventions.

Anahtar Kelimeler

• Non-thyroidal illness syndrome
• central hypothyroidism
• low fT4

Santral hipotiroidi tanısında karşılaşılan zorluklar

Öz

Amaç: Serum serbest tiroksin (fT4) seviyesindeki düşüş, yetersiz tiroid uyarıcı hormon (TSH) artışıyla birlikte, santral hipotiroidizm (SH) veya tiroid dışı hastalık sendromu (NTIS) belirtisidir. Tedavi yaklaşımlarındaki farklılıklar nedeniyle iki klinik durum arasında ayrım yapmak çok önemlidir. Bu çalışmada, iki klinik durumu ayırt edebilmek için ipuçları elde etmeyi amaçladık. Gereç ve yöntem: Bu retrospektif çalışmaya, düşük fT4 ve TSH düzeyinin 10 mIU/L'nin altında olması nedeniyle pediatrik endokrinoloji polikliniğine yönlendirilen 650 çocuk ve adölesan alındı. fT3, fT4 ve TSH en az 2 hafta arayla 3 kez ölçüldü ve üçüncü ölçümde serum fT4 düzeyinde artış olmayan hastalara SH tanısı konuldu. SH'li hastalara levotiroksin başlandı. Levotiroksin kesildikten sonra, fT4 normal saptanırsa geçici SH; düşük saptanırsa kalıcı SH tanısı konuldu. Kalıcı SH gelişimini etkileyen faktörler araştırıldı. Bulgular: Elli üç hastanın (25 kadın, 28 erkek) 6 hafta boyunca serum fT4 düzeyi düşük ve TSH düzeyi 10 mIU/L'nin altında idi. Kalıcı SH'li hastaların fT4 ve TSH seviyelerinin önemli ölçüde düşük olduğu, geçici SH'li hastalarda ise fT3'ün daha düşük olduğu bulundu (p<0,001, p=0,03, p=0,01, sırasıyla). Düşük fT4, kalıcı SH olasılığının artmasıyla bağımsız olarak ilişkili olan tek önemli öngörücüydü (OR:-0,52, %95 CI:0,3-0,9, p=0,014). Ayrıca, fT4 kesme değerinin 8,5 ng/L'nin altında olması kalıcı SH için tanısal idi (Duyarlılık: %75, özgüllük: %71). Sonuç: fT4 seviyelerinin 8,5 ng/L'nin üzerinde olması kalıcı SH olasılığı düşürmektedir. Bu hastalarda uzun süreli takip, gereksiz laboratuvar incelemeleri ve tedavi edici girişimlerin önüne geçerek maliyet açısından etkili bir önlem olacaktır.

Anahtar Kelimeler

• Tiroid dışı hastalık sendromu
• santral hipotiroidizm
• düşük fT4

Kaynakça

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