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The lack of overt signs and symptoms and controversies surrounding the thyroid stimulating hormone (TSH) reference range variability make the management of subclinical hypothyroidism (sHT) a challenge.
Because muscle cramps and weakness have been noted in subclinical hypothyroidism, histological skeletal muscle examination may be of diagnostic significance, as the presence of abnormalities would substantiate a significant consequence of the mild thyroid failure presumed to be present in the individual with subclinical hypothyroidism.
The objective of this study was to investigate the ultrastructural and histological changes of skeletal muscle associated with subclinical hypothyroidism.
Skeletal muscle biopsies from the vastus lateralis were obtained from four subjects with sHT. Samples were fixed, sectioned, and stained for quantitative and qualitative electron and light microscopic analysis.
Analyses revealed characterizable morphological and ultrastructural alterations and quantitative mitochondrial variations between subjects, indicative of skeletal muscle mitochondrial dysfunction in subclinical hypothyroidism patients.
For the 4 subjects, mean mitochondrial perimeter (MP) was 1.09 ± 0.312 ?, mean mitochondrial area (MA) was 0.10 ± 0.05 ?², and mean mitochondrial volume density was 1.92 ± 0.95.
Conclusions: The observed and quantified mitochondrial alterations and the noted morphological and ultrastructural alterations identify previously undocumented pathological skeletal muscle alterations associated with subclinical hypothyroidism.
The observed morphological and ultrastructural alterations lend support to a trend of progression of subclinical hypothyroidism into overt hypothyroidism as a result of mitochondrial dysfunction and associated metabolic shift.
The identification of these skeletal muscle alterations as sequelae of subclinical hypothyroidism may lend convincing objective evidence of a pathophysiologically significant abnormality in patients with subclinical hypothyroidism.
If so, this should diminish the substantial resistance to treatment of these patients at an early stage of disease and attenuate the progression to overt hypothyroidism.
Source: Thyroid Science, June 2009; 4(6):CR1-8. Dunn ME, Hennessey JV, Cosmas AC, Lamont LS, Manfredi TG. Department of Kinesiology, University of Rhode Island, Kingston, Rhode Island; Division of Endocrinology, Rhode Island Hospital, Brown University School of Medicine, Providence, Rhode Island, USA. [E-mail: email@example.com]