The Impact of Overt and Subclinical Hyperthyroidism on Skeletal Muscle
Abstract
OBJECTIVE: Patients with overt hyperthyroidism (OH) commonly have proximal limb muscle weakness that improves after correction of hyperthyroidism. It is unclear, however, if patients with milder degrees of hyperthyroidism (referred to as subclinical hyperthyroidism or SCH) may also have a degree of muscle weakness. This may have clinical relevance as SCH patients are often elderly and may therefore have concurrent sarcopenia of aging and would represent a previously unrecognized complication of SCH. DESIGN: We measured both thigh strength and cross-sectional area in patients with OH (n = 30) or SCH (n = 24), both prior to treatment of hyperthyroidism and again at 6-9 months after the restoration of a euthyroid state. Euthyroid controls (n = 48) were studied at similar time intervals. MAIN OUTCOME: Prior to treatment, both knee flexor and extensor muscle strength was reduced in both patients with OH and SCH compared to controls (p < 0.05). After treatment all strength measurements improved in the OH group (p < 0.01) while in the SCH group the majority of muscle strength measurements improved (p < 0.05). Midthigh muscle cross-sectional area was reduced in both the OH and SCH group at baseline (p < 0.05) compared to controls and increased significantly following treatment (p < 0.05). There were no significant changes in any parameter in the euthyroid control (EC) group during the study period. CONCLUSIONS: The finding that muscle strength and cross-sectional area are reduced in SCH and improved after treatment lends support for the clinical decision to treat rather than observe this condition. This may have particular relevance to certain SCH patient groups including the elderly who are prone to falls and athletically active younger patients who require optimal skeletal muscle function.
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An excess of thyroid hormone can affect neuromuscular function and muscle strength.
“An excess of thyroid hormone can also affect neuromuscular function and muscle strength23”
From Levothyroxine dose and risk of fractures in older adults: nested case-control study (2011) · cites this paper as [23]
Excess thyroid hormone can increase the risk of arrhythmias and muscle weakness in older people, which can contribute to a greater risk of falls.
“Excess thyroid hormone can also increase the risk of arrhythmias24 25 and muscle weakness23 in older people, which can contribute to a greater risk of falls.”
From Levothyroxine dose and risk of fractures in older adults: nested case-control study (2011) · cites this paper as [23]
Muscle strength is restored after normalization of thyroid hormones in young or non-elderly subjects with hyperthyroidism.
“few studies in young or non-elderly subjects have demonstrated reduced muscle strength, which is restored after normalization of thyroid hormones (114–119).”
From Levothyroxine therapy in elderly patients with hypothyroidism (2021) · cites this paper as [116]
In young or non-elderly subjects, hyperthyroidism is associated with reduced muscle strength.
“few studies in young or non-elderly subjects have demonstrated reduced muscle strength, which is restored after normalization of thyroid hormones (114–119).”
From Levothyroxine therapy in elderly patients with hypothyroidism (2021) · cites this paper as [116]
In cohort studies, subclinical hyperthyroidism or lower serum TSH have been associated with many involutional disease states including dementia, osteoporosis, AF, muscle weakness, low bone density, and fracture.
“in cohort studies, subclinical hyperthyroidism or lower serum TSH have been associated with many involutional disease states including dementia, osteoporosis, AF, muscle weakness, low bone density, and fracture (12–14, 18, 20, 48, 49).”
From Serum Thyroid Function, Mortality and Disability in Advanced Old Age: The Newcastle 85+ Study (2016) · cites this paper as [49]
Another uncontrolled study showed an increase in muscle mass and muscle strength in middle-aged women with SH after treatment with RAI or thyroidectomy.
“Another uncontrolled study showed an increase in muscle mass and muscle strength in middle-aged women with SH after treatment with RAI or thyroidectomy (426).”
From 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis (2016) · cites this paper as [426]
The evidence rests only with small uncontrolled studies that have shown improvements in cardiac structure and function, heart rate and the frequency of premature atrial and ventricular beats, bone mineral density, and muscle strength.
“Thus, the evidence rests only with small uncontrolled studies that have shown improvements in cardiac structure and function, heart rate and the frequency of premature atrial and ventricular beats, bone mineral density, and muscle strength (393)(394)(395)(396)405,(414)(415)(416)(417)426).”
From 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis (2016) · cites this paper as [426]
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References 31 · Cited by 155
- Authors
- Brennan, M. D., Powell, C., Kaufman, K. R., Sun, P. C., Bahn, R. S., & Nair, K. S.
- Affiliations
- Mayo Clinic (US)
- National Yang Ming University (TW)
- Venue
- Thyroid
- Publisher
- SAGE Publications
- Published
- 2006-04
- Volume
- 16
- Issue
- 4
- Pages
- 375-380
- ISSN
- 1050-7256 (ISSN-L)
- 1557-9077
- OpenAlex
- W1982650718
- Cited by
- 155
- References
- 31
- Citations by year
- 2026: 6 · 2025: 6 · 2024: 9 · 2023: 12 · 2022: 13 · 2021: 13 · 2020: 16 · 2019: 11 · 2018: 6 · 2017: 8 · 2016: 5 · 2015: 7 · 2014: 9 · 2013: 3 · 2012: 6
- FWCI
- 2.70
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Thyroid (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Medicine › Surgery › Thyroid and Parathyroid Surgery
- Health Sciences › Medicine › Pathology and Forensic Medicine › Ophthalmology and Eye Disorders
- Keywords
- subclinical hyperthyroidism, overt hyperthyroidism, skeletal muscle weakness, muscle strength, thigh muscle cross-sectional area, knee flexor and extensor strength, hyperthyroidism treatment, fall risk
- MeSH terms
- Adolescent, Adult, Aged, Aged, 80 and over, Female, Humans, Hyperthyroidism, Male, Middle Aged, Thyrotropin, Muscle, Skeletal, Muscle Weakness, Muscle Strength
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