Lupus panniculitis

Patients with lupus erythematosus may rarely present with prominent involvement of the subcutaneous tissues, a condition that has been termed lupus panniculitis or lupus profundus. Lupus panniculitis reveals subcutaneous plaques and indurations, mostly located on the extremities, which can simulate clinically and histopathologically those observed in subcutaneous T-cell lymphoma (see Chapter 5) (Fig. 20.20) [57]. Antinuclear antibodies and other criteria for the diagnosis of systemic lupus erythematosus may be absent in some cases. Histology shows a predominantly lobular pan-niculitis, often with concomitant presence of broadened fibrotic septa. A useful feature for the differentiation of subcutaneous T-cell lymphoma from lupus panniculitis is the presence in the former of so-called 'rimming' of fat cells by pleomorphic atypical T lymphocytes that are positive for proliferation markers. It must be remembered that rimming of fat lobuli by lymphocytes is not a diagnostic feature per se, as it can be observed in several benign and malignant lymphoid infiltrates with involvement of the subcutaneous fat. In contrast to subcutaneous T-cell lymphoma, B cells, plasma cells and germinal centres are usually a prominent feature in lupus panniculitis (Figs 20.21 & 20.22). Moreover, the

Fig. 20.21 Lupus panniculitis. Lobular panniculitis with dense lymphoid infiltrates and fibrotic septa.
Tcell And Cell Sle
Fig. 20.22 Lupus panniculitis. Note mixed-cell infiltrate with lymphocytes, histiocytes, neutrophils and several plasma cells (detail of Fig. 20.21).

dermo-epidermal junction may show features of lupus erythematosus (interface dermatitis). Analysis of TCR gene rearrangement reveals polyclonal populations of T lymphocytes in lupus panniculitis, in contrast to subcutaneous T-cell lymphoma where monoclonality of T lymphocytes is found in most cases.

Treatment of lupus panniculitis is similar to that of other variants of lupus erythematosus. The lesions respond well to systemic steroids but recurrences are the rule.

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