Human orf is usually considered a rare disease caused by a virus belonging to the paravaccinia subgroup of pox viruses and transmitted to man from sheep and goats. This paper presents 119 new human cases with epidemiological, clinical, histopathological and ultrastructural findings. Erythema multiforme was found to be a common complication of human orf. Other complications tended to be caused by overtreatment. Electron microscopy of negatively stained suspensions from lesions was found to be the best and most rapid diagnostic method available.

Hürthle cell transformation found in 2 nodular goiters, 2 cases of Hashimoto's thyroiditis, 4 follicular adenomas, 3 follicular carcinomas, 2 papillary carcinomas and 1 anaplastic carcinoma were studied by transmission electron microscopy, scanning electron microscopy and immunocytochemistry. Ultrastructural features of Hürthle cells were identical in non-neoplastic and neoplastic lesions. Cells crammed with mitochondria, showing abnormalities in size, shape and content were prominent in most cases. The presence of distinct smooth-surfaced cells interspersed with cells with many microvilli is almost a pathognomonic scanning electron microscopic feature of benign and malignant Hürthle cell lesions. Most Hürthle cells stained positively for thyroglobulin in all cases, but no immunoreactivity for CEA and calcitonin was found.

An unusual case of poorly differentiated carcinoma of the thyroid is reported. The tumor occurred in a 60-year-old man, who died with widespread metastases 5.5 years after primary treatment. The unencapsulated tumor measured 8 X 5 X 9.5 cm and was composed of columnar cells. Two to three mitotic figures per 10 high-power fields were present. The cells were thyroglobulin positive and not stained for calcitonin and carcinoembryonic antigen (CEA). The light microscopic appearance was similar to that of a metastasis from a carcinoma of the bowel. The authors conclude that columnar cell carcinoma is a separate type of thyroid carcinoma that shares the clinical properties of both follicular and papillary carcinoma and carries a poor prognosis. However, for practical purposes, the authors think that the tumor should be included in the category of poorly differentiated thyroid carcinomas together with the so-called insular carcinomas, mucoepidermoid carcinomas, and mucinous carcinomas.

Of 52 consecutive papillary carcinomas of the thyroid, the following cases were included in this study: one Hürthle cell papillary carcinoma, one papillary carcinoma with foci of Hürthle cells, and 10 cases of papillary carcinoma with abundant mitochondria (volumetric density of mitochondria greater than or equal to 20%). All cases were studied by light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and immunocytochemistry. Our results showed that papillary carcinomas mainly or exclusively composed of Hürthle cells are very rare; that Hürthle cell papillary carcinomas of the thyroid share the biologic characteristics and blend insidiously with the so-called mitochondrion-rich papillary carcinomas; that TEM and SEM can provide useful evidence for achieving the differential diagnosis between Hürthle cell and so-called mitochondrion-rich papillary carcinomas; and that immunocytochemical studies are useless in the aforementioned differential diagnosis.