This is a fictional, illustrative case created for education. It is not medical advice, diagnosis, or treatment, and does not describe a real person.

Her TSH was normal. Her cells were still asking for thyroid hormone.

Ciara, 49, took levothyroxine for six years and heard the same thing every year: your TSH is normal. She still felt cold, foggy, exhausted, and stuck in a body that would not respond. Her genetics explained the missing piece: normal TSH does not always mean thyroid effect is adequate in the tissues.

Persona

Ciara, 49, Female, Irish, Social worker.

Ciara was diagnosed with hypothyroidism six years ago and started on levothyroxine (T4). At every annual review her family doctor shows her the TSH result — currently 1.8 mIU/L, well within the reference range — and confirms her thyroid is well-controlled. She has every symptom she had before diagnosis: persistent fatigue, 18 lb of weight gain she cannot shift despite eating carefully, brain fog that makes her question whether she can continue in her demanding job, cold intolerance, low mood, constipation, and dry skin. She has been referred to psychiatry for depression. She does not believe she is depressed — she believes she is physically ill and cannot get anyone to listen.

Family history: Mother: hypothyroid on levothyroxine, similarly symptomatic despite being told TSH was normal. No known cardiac or neurological history.

Clinical picture

Symptoms

Labs

Medications

Supplements

Lifestyle

Genetics

Six years of normal results. Six years of the same symptoms.

Ciara was diagnosed with hypothyroidism at 43 after years of fatigue and weight gain. Starting levothyroxine felt like the answer. Within a few months her TSH was normal. Her family doctor was pleased. The symptoms did not change. The morning commute still felt like a marathon. The weight did not move despite careful eating. The brain fog made her question whether she could continue as a social worker. At every annual review she raised the same concerns. At every annual review she was shown the TSH number and told the thyroid was controlled. By year four she had been referred to psychiatry and tried an antidepressant for six months. Nothing changed. She did not feel depressed. She felt physically ill and unheard.

Normal TSH does not always mean enough thyroid effect

TSH is produced by the pituitary gland as a signal to the thyroid. When the pituitary has enough T3, the active form of thyroid hormone, TSH settles into the normal range. The key word is pituitary. TSH shows whether the pituitary is satisfied. It does not directly prove that muscle, brain, fat, and heart tissue are getting the same active thyroid effect. For most people, that distinction may not matter much. For Ciara, it was the missing clue.

Her cells may not be converting enough T4 into T3

Ciara's medication supplies T4, but her brain, muscles, and fat cells may struggle to turn it into usable T3. She carries two copies of the DIO2 Thr92Ala variant, which points to reduced conversion in those tissues. Her active T3 sits at the very bottom of the normal range, and her reverse T3 is elevated — an inactive form that can compete at the receptor without turning the signal on. Her TSH can look perfect because the pituitary is satisfied while other tissues may still be under-supplied.

The mood symptoms were downstream of the thyroid clue

Ciara's low mood and brain fog were not separate mysteries. A reduced DIO1 pattern can lower the active T3 signal measured in blood, while DIO2 can limit conversion inside key tissues. Her BDNF variant adds another reason her brain may notice that shortfall: T3 helps support pathways involved in memory, focus, and mood. Antidepressants target different systems. If tissue T3 is still inadequate, treating the mood symptoms alone can miss the cause.

Five conversations and interventions — in order of priority

Ciara's 14-day nutritional support check-in

Daily energy, mental clarity & cold intolerance — while awaiting T4/T3 review. Ciara started selenium and iron supplementation on day 1 while waiting for her endocrinology appointment to discuss T4/T3 combination therapy. Nutritional cofactors work slowly; the first week showed little change. By day 9 the first noticeable shift arrived. The lab recheck and medication review are the next step.