To the Editor.
—In the April 1987 issue of the Archives, Harada et al1 report the observed association of hyperparathyroidism caused by an adenoma and myotonic dystrophia in two cases. They suggest a possible pathogenic interrelation through changes in the cell membrane permeability to calcium evidenced in myotonic dystrophia and as a triggering event in the derangement of the regulating function of the parathyroid glands. A casual coincidence in both clinical entities is not ruled out.In support of the possible pathogenic relationship, we would like to report another case in a 40-year-old man with clinically and electromyographically proved myotonic dystrophia, who was admitted to our hospital because of bone pain. Hyperparathyroidism caused by a 2.5×2.0-cm adenoma was demonstrated, with histologic confirmation at surgery. A contralateral parathyroid gland was resected, and a biopsy was performed on a third parathyroid gland, giving evidence of normal histologic findings. The preoperative parathyroid