The objective of the present investigation was to study quantitatively C cells in Hashimoto's thyroiditis (HT) by analyzing 22 thyroids obtained at autopsy or thyroidectomy from 16 patients with thyroiditis and from 6 normal subjects. Six different areas were sampled on average and labeled with a monoclonal anticalcitonin antibody by immunohistochemistry using the avidin-biotin-peroxidase complex. Normal thyroids from adult patients with no thyroid disease were used as control. C cells were counted in 1 cm2 fields and the mean number of cells per field was calculated. Data were analyzed statistically by the Mann-Whitney test. The inflammatory process detected in cases of HT was usually moderate (50%) and the number of C cells ranged from 0 to 12.2 per 1 cm2 field. The number of C cells in normal thyroids ranged from 20 to 148 per 1 cm2 field, with a median of 35.2 cells per field. The results demonstrate a significant decrease in C cell number in HT compared with normal thyroids, indicating that the inflammatory process causes destruction of both follicular and C cells, which are replaced by fibrosis.

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