Panniculitis. Part I. Mostly septal panniculitis.

The panniculitides represent a group of heterogeneous inflammatory diseases that involve the subcutaneous fat. The specific diagnosis of these diseases requires histopathologic study because different panniculitides usually show the same clinical appearance, which consists of subcutaneous erythematous nodules on the lower extremities. However, the histopathologic study of panniculitis is difficult because of an inadequate clinicopathologic correlation, and the changing evolutionary nature of the lesions means that biopsy specimens are often taken from late-stage lesions, which results in nonspecific histopathologic findings. In addition, large-scalpel incisional biopsies are required. However, we believe that by obtaining appropriate biopsy specimens and with adequate clinicopathologic correlation, a specific diagnosis may be rendered in most cases of panniculitis. It must be accepted that all panniculitides are somewhat mixed because the inflammatory infiltrate involves both the septa and lobules; however, in general the differential diagnosis between a mostly septal and a mostly lobular panniculitis is straightforward at scanning magnification. Mostly septal panniculitides with vasculitis include leukocytoclastic vasculitis involving the small blood vessels of the septa; superficial thrombophlebitis resulting from inflammation and subsequent thrombosis of large veins of the septa; and cutaneous polyarteritis nodosa, which is a vasculitis involving arteries and arterioles of the septa of subcutaneous fat with few or no systemic manifestations. Often septal panniculitides with no vasculitis are the consequence of dermal inflammatory processes extending to the subcutaneous fat, such as necrobiosis lipoidica, scleroderma, subcutaneous granuloma annulare, rheumatoid nodule, and necrobiotic xanthogranuloma. However, in other cases, the inflammatory process is primarily located in the fibrous septa of the subcutis with or without involvement of the overlying dermis. The most frequently seen septal panniculitis is erythema nodosum, which, in fully developed lesions, is characterized histopathologically by Miescher's radial granulomas in the septa.

Epithelioid blue nevus: a rare variant of blue nevus not always associated with the Carney complex.

Epithelioid blue nevus is a rare variant of blue nevus that has been recently described in patients with Carney complex. Some of the patients with Carney complex have multiple epithelioid blue nevi and a familial history of similar lesions is often recorded. Epithelioid blue nevus consists of an intradermal melanocytic nevus composed of polygonal epithelioid cells laden with melanin. Neoplastic cells show no maturation at the base of the lesion and, in contrast with the usual stromal changes in blue nevi, epithelioid blue nevus exhibits no fibrosis of the dermis. We have studied three cases of epithelioid blue nevus in three patients with no evidence of Carney complex. The lesions were solitary and there was no family history of similar lesions. Therefore, epithelioid blue nevus is a distinctive variant of blue nevus that may also appear as a sporadic lesion and is not always associated with Carney complex.

Striated muscle: a normal component of the dermis and subcutis in many areas of the face.

Striated muscle is typically not mentioned in histology chapters of most dermatology and dermatopathology books. In others, authors only speak of its presence in the dermis or subcutis but do not provide any details about its quantity, distribution, or orientation. In the course of an investigation concerning regional histologic variations of the skin, the presence of striated muscle fibers (StrMFs) has been a noteworthy feature of many areas of the face. Striated muscle fibers are a normal constituent of the dermis of the eyebrow (few and deep fibers); eyelid and nose (excluding the nasal tip) (numerous and deep fibers); and lips and chin (numerous, vertical, and more superficial fibers). They are also found in the subcutis of all these areas with some differences in density and distribution among them. Striated muscle fibers form a compact layer beneath the subcutaneous fat on the forehead and cheek, but because of their deep location, they are rarely included in cutaneous biopsy specimens of the latter area. Mainly based on the presence of StrMFs in the dermis, an algorithm to accurately determine the location of biopsy specimens from the face has been elaborated. With the aid of other features such as the type of hair follicles and the presence and degree of solar elastosis, the sex and approximate age of the patient can be established in many cases. Some practical and scientific consequences of these findings are discussed.

Intravascular and diffuse dermal reactive angioendotheliomatosis secondary to iatrogenic arteriovenous fistulas.

Reactive angioendotheliomatosis is a rare benign process that has been mainly described in patients with systemic infections, such as subacute bacterial endocarditis or tuberculosis, and in association with intravascular deposition of cryoproteins. Histopathologically, it is characterized by a proliferation of endothelial cells within vascular lumina resulting in the obliteration of the involved vessels. Another rare variant of reactive angioendotheliomatosis has been described in the lower extremities of patients with severe peripheral vascular atherosclerotic disease. It consists of violaceous and purpuric plaques histopathologically characterized by diffuse proliferation of endothelial cells interstitially arranged between collagen bundles of the reticular dermis. This second variant has been named diffuse dermal reactive angioendotheliomatosis. We report two patients with reactive cutaneous angioendotheliomatosis appearing distally to arteriovenous fistulas used for hemodialysis because of chronic renal failure. The first patient showed intravascular reactive angioendotheliomatosis, while the second one had purpuric plaques that were characterized histopathologically by diffuse dermal angioendotheliomatosis. Both patients showed an arteriovenous "steal" syndrome with distal ischemia, and it is possible that a local increase of vascular endothelial growth factor, as is the case in hypoxia situations, induces the endothelial proliferation. To the best of our knowledge, cutaneous reactive angioendotheliomatosis has not been previously described in association with arteriovenous shunts.

Acrolocalized acquired cutis laxa.

A 55-year-old man presented with a 14-year history of loose, redundant skin on the palmar aspects of the finger tips and toe pulps, which gave a peculiar 'chewing gum' appearance. Skin biopsies of involved areas showed a normal appearance, and only a discrete decrease in the elastic fibres could be identified with an elastic tissue stain. Ultrastructural examination, however, demonstrated marked fragmentation and degeneration of the elastic tissue. Localized cutis laxa in an acral distribution, was fully developed at presentation. He gave a history of repeated episodes of swelling and urticaria of the involved areas, which we regard as being the initial inflammatory stages of this disease process.

Multiple trichodiscomas: histogenetical observations.

A 23-year-old man with multiple trichodiscomas on his face is described. Four papules were histologically examinated, and all of them showed similar findings, a dermal fibrovascular proliferation with abundant ground substance between collagen bundles and an absence of elastic fibers. We found no evidence to establish a relationship between trichodiscomas and hair disk, and, in our opinion, these lesions should be included into the spectrum of hyperplasia of the adventicial dermis.

Angioleiomyoma within a histiocytoma.

We report an angioleiomyoma developed within a cellular histiocytoma on the calf of a 77-year-old man. The lesion consisted of a spherical nodule with two well-defined concentric areas. The outer circular area was a cellular histiocytoma and the inner central area consisted of an angioleiomyoma. Immunoperoxidase investigations for desmin demonstrated positivity in the angio-leiomyoma, whereas the histiocytoma remained negative. Serial sections of the lesion failed to demonstrate a connection between the angioleiomyoma and a normal vein which could have been trapped by the histiocytoma. The angioleiomyoma may have originated from a vessel in the histiocytoma.