Achille Civatte examined sections of tissue of a specimen of skin taken from the patient of Degos et al.¹ He described the changes in these words: ". . . beneath an atrophic and hyperkeratotic epidermis, a dermal zone extremely poor in cells reaching as far as the hypodermis, with a few discrete areas of lymphoid infiltration. There were few thrombosed vessels with surrounding hyaline degeneration and neighboring sweat glands showing necrosis. The nerves seemed intact." For Degos and Civatte, the differential diagnosis of malignant atrophic papulosis histopathologically included dermatitis artefacta, syphilis, microemboli, scleroderma, disseminated lupus erythematosus, tuberculides, parapsoriasis varioliformis, and anetoderma.^1,20

Magrinat also scrutinized histopathologic findings in the skin of patients with Degos' disease and his observations were recorded in these lines: "the skin shows an inverted cone of necrobiosis with the hyperkeratotic atrophic epidermis at the base and a thrombosed vessel in the dermal apex. The cone itself consists of a largely acellular area showing dermal edema and accumulation of acid mucopolysaccharide. There is scant perivascular dermal infiltrate consisting almost entirely of mononuclear cells, primarily lymphocytes. Affected vessels show endothelial swelling and proliferation. Platelet-fibrin thrombi may be found occluding the lumen. There is no leukocytoclasis, no disruption of the internal elastic lamina, no involvement of the media and adventitia and no granulocytic infiltrate."¹³

Black⁴ and Feuerman²⁵ observed marked accumulation of mucin in early skin lesions of Degos' disease. Once such a lesion had become well established, however, mucin was confined to the margin of the central eosinophilic zone.^4,25 In skin lesions, it often is very difficult, even with the benefit of serial sections, to detect vascular occlusion.⁴ Once visceral involvement has occurred, infarcts in small arteries and arterioles of internal organs are much more conspicuous than in skin lesions.⁴ No "necrotizing" vasculitis, granulomas, or calcification has been noted at autopsy, neither in the skin nor in other organs.²⁷

Soter et al. examined sections of biopsy specimens obtained from lesions in the skin of three patients with Degos' disease and noted these changes: hyperkeratosis, focally elongated rete ridges that alternated with foci of atrophic epidermis, vacuolization of the dermo-epidermal junction, necrotic keratocytes, edema of the papillary and reticular dermis, mucin in the reticular dermis, extravasated red blood cells, and a perivenular infiltrate of mononuclear inflammatory cells mostly, particularly prominent at the periphery of the acellular dermis.²⁸

Su et al. studied sections from 27 biopsy specimens removed from skin lesions of nine patients with Degos' disease. The most consistent finding was an infiltrate of lymphocytes and histiocytes in a dermis and subcutaneous tissue devoid of vasculitis. The wedge shape of infarction, mentioned so often as a classic feature of Degos' disease, was present in only three of the 27 specimens, and then mostly in older, well-formed lesions marked by umbilication centrally. Thrombosis of arterioles in the deep part of the dermis or in the subcutaneous fat could be appreciated in two specimens only.¹⁴ Other authors agree that a sparse perivascular infiltrate of lymphocytes may be accompanied by endothelial proliferation and sometimes by thrombosis, but no true leukocytoclastic vasculitis is encountered.^29,30 Barlow et al., however, claimed to have noted a slight infiltrate of neutrophils accompanied by leukocytoclasis in arteries in the bowel and the brain.³¹

Recently, Grilli et al. told of a patient with characteristic clinical and histopathologic findings of Degos' disease, as well as features of "sclerosing panniculitis."³² The authors denied the possibility of lupus profundus for these reasons: ". . .our patient had neither clinical nor laboratory evidence of systemic lupus erythematosus. Furthermore, histopathologically, lesions of lupus panniculitis characteristically show a dense inflammatory infiltrate with abundant plasma cells and occasional lymphoid follicles formation, features that were not present in the biopsy of our patient. Also, direct immunofluorescence studies in cutaneous lesions yielded negative results."

Confusion abounds in the literature in regard to histopathologic findings in Degos' disease. Most authors agree that the main changes in a fully developed lesion is a wedged-shaped zone of sclerosis in the dermis, the apex of the wedge pointing in the direction of the subcutaneous fat, an atrophic epidermis, and deposits of mucin in the reticular dermis especially. Many other features have been mentioned, including perivascular infiltrates of inflammatory cells without any sign of vasculitis,^{4,13,14,18,20,28,29,30} lymphocytic vasculitis,^12,14,28 perineural and intraneural infiltrates of lymphocytes,²⁸ neutrophilic vasculitis,³¹ thrombosis with vasculitis,³¹ thrombosis without vasculitis,^14,20,29,30 and sclerosing panniculitis.³² The reasons for the differences are not known, but some of them may be attributable to different findings at different stages in the chronologic course of a lesion; others may be mere misperception or misconception.

Harvell et al. traced the sequence of histopathologic changes in papules of Degos' disease, designating the stages "early," "fully developed," and "late." According to them, an early papule is skin-colored, slightly raised, and measures less than 1 cm in diameter. It is typified histopathologically by an infiltrate of lymphocytes that is superficial and deep perivascular, periadnexal epithelial, and perineural, and by deposits of mucin in the reticular dermis, that constellation of findings causing a lesion to resemble that of tumid lupus erythematosus. In the center of a lesion, vacuolar alteration is present in company with a few necrotic keratocytes along the dermo-epidermal junction.¹⁷

A fully developed papule has an umbilicated porcelain-white center surrounded by an erythematous rim. Histopathologically, changes are more prominent at the dermo-epidermal interface, melanin is "incontinent," the epidermis is atrophic, and a zone of sclerosis in the papillary dermis resembles "in miniature" what is seen at an early stage of lichen sclerosus et atrophicus. In contrast to lichen sclerosus, however, the elastic fibers in Degos' disease remain intact. The changes at the interface are confined to the center of the lesion and are said to correspond to the porcelain-white zone seen clinically. Other features include prominent infiltration by lymphocytes of the media and subendothelium of venules, mural deposits of fibrin, and intraluminal thrombi.¹⁷ In addition, a periadnexal and interstitial infiltrate composed mostly of neutrophils, but also of eosinophils, has been commented on by many authors,^24,28,31,34 including Köhlmeier in his seminal article.² Similar changes occur at an early stage of lupus erythematosus.

A lesion at a late stage is flat, slightly indurated, and porcelain-white, but devoid of any sign of surrounding erythema. The lesion is marked by a well-developed wedge-shaped zone of sclerosis flanked in the upper half of the dermis by a sparse infiltrate of lymphocytes and overlain by an atrophic epidermis whose stratum corneum is compactly orthokeratotic. The amount of mucin, especially in the zone of sclerosis, is less than in a fully-developed lesion. Many blood vessels are said to have a thick wall and a sclerotic or hyalinized cuff. Although sclerosis in the upper part of the dermis usually is pronounced and extends well into the reticular dermis in a somewhat wedge-shaped pattern, it sometimes may be bandlike.¹⁷

A feature common to all stages was change along the dermo-epidermal interface in the center of a lesion.