Subcutaneous Panniculitislike Lymphoma

Synonyms:

Subcutaneous lymphoma, cytophagic histiocytic panniculitis

Etiology:

Unknown

Associations:

Bleeding diathesis

Clinical:

Hemorrhagic plaques and nodules, abdomen and extremities

Histology:

Dense lymphoid infiltrate in subcutis with hemorrhage and necrosis

IHC repertoire:

CD3, CD4, CD8

Staging:

Systemic workup required to assess extent

Prognosis:

Bimodal; 5-year survival

Adverse variables:

Unknown

Treatment:

Systemic chemotherapy

Subcutaneous panniculitis-like lymphoma (SPL) occurs primarily in younger adults, but can arise in persons of any age. The usual presentation is that of an ulcerative and hemorrhagic panniculitis, presenting as multiple ery-thematous nodules often involving the lower extremities and abdomen (Figure 10.1). Coagulopathies are frequently observed in these patients. In addition, many of these patients display constitutional symptoms such as weight loss, fever, and fatigue. This disease may represent what was previously known as cytophagic histiocytic pannicu-litis, at least in some cases (1). The prognosis is ominous for some patients with the disease, while others tend to have a more indolent course (2). Fatal leukemic transformation has also been reported in these patients (3). While the parameters that affect the ultimate course of the disease and prognosis have not been fully elucidated, there have been preliminary attempts at developing criteria for those with a more favorable prognosis (4).

The epidermis and superficial dermis are unremarkable in most cases of SPL, so a deep biopsy is required to establish a diagnosis. An infiltrate of atypical lymphocytes is present within the deep reticular dermis and throughout the subcutis (Figure 10.2).

The infiltrate is present diffusely within the lobules of adipocytes, as well as within the fibrous septa, and may demonstrate transmural invasion of blood vessels. Atypical lymphocytes are admixed with eosinophils and large histiocytes, some of which demonstrate emperipolesis, appearing as "bean-bag" cells. The lymphocytes are slightly enlarged and hyperchromatic, but rarely display marked cytologic atypia (Figure 10.3).

In some cases, however, more vesicular, anaplastic lymphocytes are seen (2). Zonal necrosis is present in many cases, and individual cell necrosis of tumor cells is common (Figure 10.4).

Karyorrhectic debris is a common finding (3). Mitoses, including atypical forms, are commonly observed. Immu-nostains reveal SPL to be a T-cell lymphoma. In most cases, there is a predominance of CD8 + cells, but in some cases, a CD4+ proliferation has been reported. CD30 is also seen in some cases (2). Gene rearrangements can be detected in virtually all cases. T-cell gene rearrangements are reported in most cases (1,6). In some cases, the distinction from NK lymphoma can be made only on the basis of immunophenotyping (6,7).

The major differential diagnoses include reactive pan-niculitides such as erythema nodosum (EN) and erythema induratum (EI). In EN, the inflammatory infiltrate is largely confined to the fibrous septa with only slight spillage into the lobules. Zonal necrosis is not seen and the lymphocytes are not atypical. While giant cells and histiocytes may be present, large, "bean bag" cells are not present.

EI may be more difficult to separate from SPL. In EI, zonal necrosis is seen, but is usually surrounded by a palisading granulomatous response resembling tuberculosis.

Figure 10.1. Erythematous and violaceous nodules with ecchymoses on lower extremity of patient with subcutaneous T-cell lymphoma.

Histiocytes, including multinucleated forms, are present, as is a neutrophilic infiltrate. Vasculitis may also be present. However, lymphocyte atypia is not present and an abundance of dying neoplastic cells is not a feature of this entity.

It may be difficult to distinguish SPL from angiocentric lymphoma. However, the clinical presentation is usually somewhat different. In addition, the neoplastic infiltrate in angiocentric lymphoma is usually centered more in the reticular dermis, extending into the subcutis, while in SPL, the infiltrate is centered within the subcutaneous fat, in some cases pushing into the deep reticular dermis. Further, the distinction may not be essential in terms of treatment options and prognosis.

Other cutaneous lymphomas also enter into the histologic (though not usually the clinical, differential) diagnosis. Mycosis fungoides in the tumor stage may involve the subcutaneous fat, but there is also usually a dense infiltrate of neoplastic lymphocytes within the dermis and these cells may extend into the epidermis or append-ageal epithelium. Cutaneous B-cell lymphomas such as follicular lymphoma and marginal zone lymphoma may involve the subcutaneous fat; however, eosinophils are uncommon in these tumors. These B-cell lymphomas are usually centered primarily in the dermis and not in the subcutaneous fat. In addition, necrosis of the adipocytes is not commonly seen. The cytologic characteristics are also somewhat different between these B-cell lymphomas and the subcutaneous panniculitis-like T-cell lymphoma.

Lymphoma Panniculitis Like

Figure 10.1. Erythematous and violaceous nodules with ecchymoses on lower extremity of patient with subcutaneous T-cell lymphoma.

Lymphocytic Infiltrate
Figure 10.2. Low power photomicrograph depicting diffuse infiltration of the subcutaneous fat lobules by a dense lymphocytic infiltrate.

Figure 10.3. High power photomicrograph depicting small to medium-sized hyperchromatic lymphocytes located throughout the subcutaneous fat.

Figure 10.3. High power photomicrograph depicting small to medium-sized hyperchromatic lymphocytes located throughout the subcutaneous fat.

Lupus Panniculitis Disease

Lupus panniculitis may also demonstrate some histologic features in common with SPL. In lupus, zonal necrosis would be most unusual, as would the presence of atypical lymphocytes and eosinophils. Lupus panniculitis invariably demonstrates a plasmacellular infiltrate, often at the periphery of the inflammatory cells, and a characteristic homogenization of the adipose tissue within the lobules.

Figure 10.4. Zonal necrosis is a helpful feature in distinguishing subcutaneous T-cell lymphoma from reactive panniclitides.

Figure 10.4. Zonal necrosis is a helpful feature in distinguishing subcutaneous T-cell lymphoma from reactive panniclitides.

Reactive Histiocytosis Subcutaneous
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