To obtain data on the relative incidence of changes in the basement membrane of small peripheral blood vessels in diabetic and nondiabetic patients, a “blind” study of skin biopsies was undertaken. Parallel to a thorough clinical and laboratory work-up, punch biopsies of skin were obtained under local block anesthesia. A number of morphological features were analyzed by light and electron microscopy and graded on a semiquantitative scale, and the basement membrane was measured with calipers. The tabulated data were then correlated with clinical information. The following conclusions may be drawn:
(a) “Capillaries” of the dorsal skin of the finger revealed a more complex structure than that seen in capillaries of muscle or loose connective tissue. This increased complexity was mainly due to incomplete reduplication of the endothelial cell wall by long abluminal cytoplasmic extensions.
(b) The fine structure of the basement membrane as well as its thickness revealed very large variations, having one of the following appearances:
(1) Homogeneous or finely fibrillar, and thin
(2) Homogeneous or finely fibrillar, and thick
(3) Finely fibrillar and lamellated
(4) Containing inclusions.
(c) Careful, unbiased evaluation of “capillaries” of control patients without family or own history or chemical evidence of diabetes and who can reasonably be classified as normal, and of diabetic patients, leads to results permitting no distinction between the two groups. No differences could be seen regarding the number of endothelial and/or pericytic cells per “capillary,” state of vascular contraction or dilatation, cytologic detail, or type or width of the basement membrane between normal controls and diabetic patients.
(d) The reasons for the variations in basement membrane thickness and appearance and in cellular structure are not known, but diabetes can probably be excluded as a specific etiologic factor.
(e) The results of this investigation again underline the importance of “blind” studies with adequate controls, especially where subjective evaluation cannot be excluded.
(f) It may be advisable to conduct similar blind studies on other capillary territories to assess in an unequivocal manner the relationship between the appearance of the endothelium and the basement membrane and specific diseases.