Validation of a simple, rapid, and economical technique for distinguishing type 1 and 2 fibres in fixed and frozen skeletal muscle.

AIMS: To produce a method of distinguishing between type 1 and 2 skeletal muscle fibres that would be more economical and reproducible than the standard ATPase method and be applicable to both fixed and frozen tissue. Because the ATPase method has been accepted as the basis for fibre identification for the past 50 years, the new method should not give significantly different results. METHODS: Isoforms of myosin correlate with isoforms of myofibrillar ATPase and an immunohistochemical (IHC) double labelling protocol was devised using monoclonal antibodies to fast and slow myosin. This required one tissue section rather than four. The results of the two methods were compared by means of morphometric analysis of skeletal muscle biopsies from 20 normal healthy volunteers. RESULTS: There were no significant differences (p = 0.57) in the percentages of type 1 (46% using the IHC method v 48% using ATPase) or type 2 fibres (54% v 52%, respectively). The 2a and 2b subtypes were distinguished easily. Analysis of variance revealed that cross sectional area (mu m(2)), diameter (mu m), form factor, and density of fibre staining (a measure of substrate-enzyme or protein) were all similar. The method worked equally well on fixed material. CONCLUSION: An IHC method based on the fast and slow isoforms of myosin shows no significant differences in fibre type analysis from the standard ATPase method although it provides important advantages because it is applicable to fixed (including archival) material, is economical and reproducible, and yields a permanent preparation.

The immunohistochemical localization of S100 in the diagnosis of papillary carcinoma of the thyroid.

In general, the diagnosis of papillary carcinoma of the thyroid is readily achieved based on a defined aggregate of histopathologic features. A papillary architecture is an important but not pivotal component of the diagnosis. The recognition of classic nuclear features is the essential diagnostic element. However, both the architectural and cytological hallmarks may be encountered in other conditions and produce problems in histopathologic interpretation. A papillary architecture may be encountered in hyperplastic areas of follicular neoplasms, multinodular goiter, and Graves' disease. Moreover, there may be scattered cells within several thyroid lesions that display some of the nuclear characteristics of papillary carcinoma. The distinction of these lesions from papillary carcinoma has important implications for clinical management. Thus, the availability of supportive diagnostic evidence would be helpful. In the authors' experience, the strong expression of S100 is of value in identifying papillary neoplasia and distinguishing it from examples of papillary hyperplasia. It is of supportive but not conclusive use in distinguishing follicular adenoma from the follicular variant of papillary carcinoma. The authors stress that the overwhelming factor in the distinction remains the identification of the nuclear characteristics of a papillary carcinoma. However, the authors have encountered several cases wherein the latter are either focal or absent for reasons addressed previously and have found immunohistochemistry a valuable adjunct to diagnosis. In examining papillary foci within Graves' disease, caution must be exercised; S100 expression is a phenomenon of the hyperplastic, hyperfunctional state.