Case Study: Fatigue with Suboptimal Thyroid Markers
Level 3, Clinical application
In brief
This illustrative case follows a 41 year old woman with fatigue whose TSH is at the upper end of the reference range with positive thyroid antibodies. It is organised around 5 decision points: whether to treat the TSH, what else could explain her fatigue, how to handle her request for T3 and a thyroid supplement, how to support her autoimmune thyroiditis, and how to monitor. Her fatigue resolved without thyroid hormone, through treating iron deficiency, sleep and perimenopausal symptoms.
A common and challenging presentation in integrated practice is the patient with persistent fatigue whose thyroid results are within the reference range but not ideal: a TSH at the upper end, perhaps positive antibodies, and a strong belief that the thyroid is the problem. This case, an illustrative composite, is organised around the decisions the practitioner and her doctor had to make.
Presentation
A 41 year old secondary school teacher reports 18 months of fatigue, brain fog, hair shedding, feeling cold and weight gain of 5 kg. Her mother and sister have hypothyroidism. Her TSH is 4.1 mU/L, within her laboratory’s reference range, with a normal free T4 and positive thyroid peroxidase antibodies. She has read that she has “functional hypothyroidism” and has been advised online to take T3 and a thyroid support supplement containing kelp. She has already started the supplement.
Other history: heavy periods for a year, periods becoming irregular, night sweats, sleeping 6 hours with frequent waking, a largely vegetarian diet low in iron rich foods, 2 coffees a day, and high work stress. No red flags.
Decision point 1: should the TSH be treated?
Considerations: a TSH of 4.1 is within range but, with positive antibodies, indicates autoimmune thyroiditis with a raised risk of future hypothyroidism. Guidelines generally do not recommend treating a TSH within the reference range. The kelp supplement may be affecting her thyroid function. Evidence does not support treating people with normal thyroid function with thyroid hormone, and overtreatment carries risks.
Decision: no thyroid hormone at this stage. Stop the kelp supplement, because excess iodine can destabilise autoimmune thyroid disease. Repeat thyroid function in 6 to 8 weeks.
Decision point 2: what else could explain her fatigue?
| Candidate | Features | Assessment |
|---|---|---|
| Iron deficiency | Heavy periods, vegetarian diet, hair shedding | Ferritin 9 micrograms per litre; haemoglobin low normal |
| Perimenopause | Age 41, irregular cycles, night sweats, poor sleep | Clinical picture |
| Poor sleep | 6 hours, frequent waking | Sleep history; night sweats contributing |
| B12 deficiency | Vegetarian; autoimmune thyroid disease associated with autoimmune gastritis | B12 normal |
| Vitamin D deficiency | Indoor work | Low |
| Coeliac disease | Associated with autoimmune thyroid disease; iron deficiency | Serology negative |
| Depression | Fatigue, brain fog | Screen: mild symptoms, no risk |
| Work stress | High demands | Present |
Decision: the most likely explanations are iron deficiency, disrupted sleep from perimenopausal night sweats and stress. These are addressed first.
Decision point 3: how to respond to her request for T3
She is disappointed not to receive thyroid treatment. The practitioner acknowledges her concern and her family history, explains that her thyroid is being monitored closely and may need treatment in future, and that her results do not currently indicate hypothyroidism. She explains that T3 in people with normal thyroid function can cause palpitations, anxiety, bone loss and heart rhythm problems. She points out the iron deficiency result and explains how strongly it could explain her symptoms. The patient agrees to address the other factors for 3 months and review.
Decision point 4: supporting autoimmune thyroiditis
- Adequate iodine from iodised salt and dairy, without kelp.
- Selenium from food; she eats eggs and occasionally fish.
- Vitamin D correction.
- Monitoring thyroid function, initially at 6 to 8 weeks and then periodically.
- Explanation that no diet or supplement has been shown to halt autoimmune thyroiditis.
The plan
- Her doctor starts oral iron on alternate days and investigates her heavy periods, offering treatment options.
- Discussion of perimenopause and options for managing night sweats with her doctor.
- Iron rich vegetarian foods with vitamin C; tea and coffee away from meals.
- Vitamin D supplementation.
- A consistent sleep schedule, cooler bedroom, caffeine before midday.
- Brief stress management techniques and a conversation about workload.
Decision point 5: monitoring
6 weeks: off kelp, her TSH is 3.2 mU/L. Haemoglobin has risen.
3 months: ferritin 38 micrograms per litre; heavy periods improved with treatment; night sweats reduced; sleeping 7 hours. Fatigue score has halved, hair shedding reduced.
6 months: she feels “more like myself than in 2 years”. TSH remains within range. Plan: annual thyroid function monitoring, earlier if symptoms change or she plans pregnancy.
Reasoning notes
- The anchoring risk was strong: patient, family history and antibodies all pointed to the thyroid. Deliberately asking “what else could this be?” revealed the iron deficiency.
- The kelp supplement was likely contributing to her thyroid results and illustrates why every product must be reviewed.
- Honest communication about why thyroid hormone was not indicated, paired with a credible alternative explanation, maintained trust.
- Monitoring, not dismissal: her autoimmune thyroiditis was taken seriously and followed.
What could have gone wrong
- Starting T3 or thyroid hormone, which might have caused side effects, masked the iron deficiency and delayed treatment of heavy bleeding.
- Continuing kelp, which might have destabilised her thyroid.
- Missing perimenopause as a cause of sleep disruption.
- Dismissing her concerns entirely, leading her to seek unregulated treatment online.
Looking beyond the thyroid
This case shows how powerful the thyroid narrative can be, and how often other, treatable causes of fatigue sit alongside it. Careful reasoning, a full assessment and honest communication allowed her to improve without unnecessary treatment, while her thyroid remains under appropriate watch.
Questions about this case
Was thyroid hormone started?
What caused her fatigue?
Why was the kelp supplement stopped?
References
- Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement. Thyroid. 2014;24(12).
- Vanderpump MPJ, Tunbridge WMG, French JM, et al. The incidence of thyroid disorders in the community: a twenty year follow up of the Whickham Survey. Clinical Endocrinology. 1995;43(1).
- Vaucher P, Druais PL, Waldvogel S, Favrat B. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012;184(11).
- Croskerry P. The importance of cognitive errors in diagnosis and strategies to minimize them. Academic Medicine. 2003;78(8).
Continue your learning
Reasoning through thyroid presentations
Thyroid cases like this are worked through in the Thyroid Disorders module of IIFM’s 6 month Functional Medicine and Clinical Nutrition program, with emphasis on reasoning and coordination.
This article is for the education of healthcare professionals. It is not a substitute for individual medical advice, diagnosis or treatment, and does not change any practitioner’s scope of practice. Regulation and guidelines differ between countries.