Thyroid issues can be congenital, neonatal, autoimmune, or related to syndromes eg Downs, Digeorge.

Note that thyroid function tests can be affected by intercurrent illness, there is also viral thyroiditis where you might get transient (usually mild) abnormalities.  So borderline results (especially if asymptomatic or other medical issues) usually just need repeated.  If results confusing, do T3.  If normal then abnormal T4 likely to be transient.  If suspicion of evolving problem, do autoantibodies (TPO antibody, Thyroid Receptor Ab (TRab)).  If progressive decline then likely to be emerging autoimmune condition.

All kinds of unusual clinical presentations in thyroid disease, for example:

• Effusions in hypothyroidism, including pericardial effusions – capillary dysfunction!? Impaired lymphatic drainage?
• Body pain
• Precocious puberty (although delayed more typical)