More about panniculitis and lymphoma

On the occasion of the journal’s publication of the latest work by Magro and colleagues on ‘Atypical Lymphocytic Lobular Panniculitis’ (ALLP), as an extension of a previous study, we thought it important to provide a framework for embracing the new contribution by these investigators. A general review of the diagnosis and management of cutaneous lymphomashasbeenpublishedrecently. In thiseditorial, we review some guiding principles for the practicing pathologist to consider more specifically when confronted with the responsibility to render diagnosis in a case whose histologic sections contain a predominantly lymphocytic lobular panniculitis. The best thing you can do first is to examine carefully the epidermis and dermis. It is ever so helpful diagnostically to find that a lymphocytic panniculitis is accompanied by vacuolar interface dermatitis with lymphocytes and necrotic keratinocytes at the dermal– epidermal junction. Also it is helpful to find that the dermis contains an excess of interstitial mucin. If one or both of these features are present, the diagnosis of lupus profundus or lupus panniculitis can be made much easier than if you focus on the panniculitis alone. In a review of lupus profundus cases, approximately half of the patients had immune complex deposition at the dermal–epidermal junction (a ‘positive lupus-band test’). This is accompanied usually,butnot always, by inflammationat thedermal– epidermal junction, vacuolar change, and necrosis of at least a few keratinocytes. One of us (NSM) has found that immunofluorescence occasionally can be helpful in the subcutis. In some cases of lupus profundus, the hyaline necrosis in the fat shows immunoglobulin deposition, especially IgG, on the periphery of the adipocytes, where there is a thin basement membrane of type IV collagen. Direct immunofluorescence studies have not been reported in ALPP. Given the confusion resulting from imprecision in terminology, we should state at the outset that historically lupus panniculitis and lupus profundus are terms that have been used synonymously. The disorder was first described by Kaposi and later by Irgang, who coined the term lupus erythematosus profundus (LEP). LEP is a disorder that may affect the subcutis alone or in continuity with changes in the dermis and epidermis in a pattern that clinically (i.e. scale, follicular plugging, dyspigmentation) and histologically resembles discoid lupus erythematosus. In the current paper, Magro et al. explore those cases of lymphocytic lobular panniculitis that do not have overlying histological changes of lupus erythematosus or clinical findings of lupus erythematosus. They defined this category previously as ‘indeterminate lymphocytic lobular panniculitis’ and now as ‘atypical lymphocytic lobular panniculitis (ALLP)’ on the basis of ‘mild atypia’ of the lymphocyte nuclei, ‘characterized by angulated and irregularly contoured nuclei with dispersed chromatin. ’ All six of their previous indeterminate cases are now included in the atypical category, and six new cases are added. Reactive and neoplastic lymphoid infiltrates, especially when composed predominantly of smallto medium-sized cells, cannot always be distinguished by morphological, immunohistochemical, or even molecular genetic analysis. In such instances, longitudinal observation of the patient’s clinical course is often invaluable in determining the best classification for each case. The mean follow-up period of patients with ALLP reported by Magro et al. was 3.4 years, with most patients exhibiting a waxing and waning course without definite evolution to lymphoma. Two patients had an isolated single episode following either an upper respiratory tract infection or a topical chemical exposure. To the extent that this follow-up period is sufficient, the fact that none of these patients have developed obvious lymphoma to date further supports the validity of the ALLP concept. Given these approaches, individual cases that defy classification will necessarily remain. In such cases, gene rearrangement analysis (GRA) is occasionally performed. The data obtained should be viewed in the context of clinical and immunohistochemical data. It is possible for example to have a B-cell clone detected when only one B cell is present within a sea of T cells. GRA is sensitive enough to be wonderful in some cases but misleading in others. GRA is potentially misleading, because it has been clearly established that some malignant disorders are not clonal in GRA and other non-malignant conditions can be clonal, e.g. lymphomatoid papulosis (LyP), pityriasis lichenoides, and atypical drug J Cutan Pathol 2004: 31: 297–299 Copyright # Blackwell Munksgaard 2004 Blackwell Munksgaard. Printed in Denmark Journal of Cutaneous Pathology