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S10C1-PANNICULITIDES
SECTION 10
Chapter 1 (HOME)
Richard J. Reed, M.D., New Orleans, LA
You are at Section 10 (Chapter 1, tier 1), a section devoted to a discussion of the histopathology of the panniculitides. Basic reaction patterns, as related to anatomic divisions of the subcutaneous tissue, will
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THE PANNICULITIDES
The panniculitides were a mystery in the 1960’s; a mystery they remain. In the ‘60’s, a classification of the panniculitides based on the character of the reacting cells and on the major distribution of the
inflammatory infiltrates was proposed. Emphasis was placed on distinctions between lesions primarily affecting the septa and those primarily affecting the lobules (Reed, RJ, Clark, WH, and Mihm, MC: Disorders of the
Panniculus Adiposus, Human Pathol, 1973; 4: 219-229). This approach was stimulated by a brief discussion in the British J Dermatology on the distribution of vessels in the fat (Bartak, P: Vascular patterns and the
pathogenesis of nodular panniculitis of the legs, Brit J Dermatol, 1970;82:15-19). It has proved to have general utility, but perhaps has stifled investigations into the basic nature of the disorders. Little insight
into the significance of the variations in the distribution of infiltrates has been forthcoming in the interval since the classification was proposed.
The septal panniculitides most likely are mediated at the level of the venous side of the vascular plexus of the septa; they are vasculitic disorders for the most part but, like the vasculitides of the dermis, a
leakage of immune complexes into the walls of vessels and then into the fibrous tissue of the septa is a likely explanation for the associated interstitial infiltrates among collagen bundles. In some examples, or at
certain stages in the evolution of a septal panniculitis, the reaction may take on a granulomatous character. The venules of the septa drain blood not only from the domain of the dermis, but also from the lobules of
adipose tissue. Granting such a relationship, it would then stand to reason that damage of the lobules likely will be associated with perivenular infiltrates of lymphocytes in the septa. In this approach, with both
lobular and septal components, the lobular changes would then take precedence in a classification of disorders that show involvement of both domains. The lack of progress in this area is evident in some of the
recent reviews of the pathology of the panniculitides.
The lobular disorders are even more of a mystery than are the septal processes. One has only to review the literature over the past 40+ years to appreciate the capriciousness of the diagnosis of a one type of lobular
panniculitis, namely Weber-Christian’s disease; the disorder has fallen in, and out, of favor several times over this interval.
Lipocytes store a variety of substances, particularly fat-soluble materials; thus, lipocytes may on occasion be antigenic.
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