Reactive paracortical hyperplasia of lymph node characterized by an increased number of interdigitating dendritic cells, Langerhans cells, and histiocytes with cytoplasmic melanin deposits and lipid vacuoles. These changes are usually associated with skin disease.

Dermatopathic lymphadenitis; lipomelanotic reticulosis.

This lesion was originally described by Pautrier and Woringer in French in 1937 but the name dermatopathic lymphadenitis was coined and published in English by Hurwitt in 1942 (1,2). Dermatopathic lymphadenopathy (DL) is usually associated with chronic dermatologic lesions and represents a lymph node reaction to the drainage of melanin and various skin antigens. In a large series of consecutive lymph node biopsy specimens, Cooper and colleagues diagnosed DL in 4.8% of specimens (3). Dermatopathic lymphadenopathy occurred twice as often in males as in females, and most patients had associated skin disease. However, 12% of patients in their study had no clinical evidence of skin disease, and similar experience is reported by others (3,4). The benign skin diseases commonly associated with DL are often exfoliative or eczematoid: toxic-shock syndrome, pemphigus, psoriasis, neurodermatitis, eczema, and atrophia senilis (2,3,4). Skin disease is often present months to years before lymph node biopsy is performed (1,2). Gould and colleagues studied over 1,000 axillary lymph nodes from 50 consecutive radical mastectomy specimens performed in women with breast cancer (4). They identified mild to moderate dermatopathic changes in approximately 15% of lymph nodes, but only one patient had active skin disease (contact dermatitis) (4). Thus, mild dermatopathic changes do not correlate as well with skin disease as full-blown DL. In addition, DL does not always correlate with contemporary skin irritation, and sometimes may reflect a history of dermatitis that has healed (4).

Dermatopathic lymphadenopathy is also a common reaction pattern in patients with mycosis fungoides (MF) and Sézary syndrome (SS). Approximately 75% of patients with MF/SS have palpable lymphadenopathy at time of diagnosis (5), explained by the presence of DL, MF/SS, or a combination of both. The presence of lymphadenopathy in MF/SS patients correlates with a poorer prognosis, regardless of histologic findings (i.e., DL versus MF/SS) (6). Possibly, this may be true because it is difficult to distinguish DL from early or minimal involvement by MF/SS. Several studies have attempted to make this distinction in lymph nodes. In cases in which involvement by MF/SS is extensive, or MF/SS focally replaces lymph node architecture, DL and MF/SS can be distinguished reliably (7). However, most authors have concluded that minimal histologic evidence of MF/SS in draining regional lymph nodes is not characteristic, and that confident distinction between DL and minimal involvement by MF/SS cannot be made using histologic criteria (8,9,10). Molecular studies allowing detection of a monoclonal T-cell population can be helpful in identifying minimal MF/SS in lymph nodes; however, the clinical significance of a small monoclonal T-cell population in the absence of obvious histologic involvement is not well established (11,12).

Axillary and inguinal lymph nodes are most commonly involved, although generalized superficial lymphadenopathy may also occur. Lymph nodes are moderately enlarged, firm, movable, and nontender. Peripheral blood eosinophilia can be present; sometimes with a percentage as high as 35% (2). Dermatopathic lymphadenopathy usually occurs with skin diseases, either benign or malignant, and many patients have pruritus.

Grossly, the cut surface of an excised lymph node may be yellow or tan with occasional brown, pigmented foci. Histologically, the architecture is generally maintained with marked paracortical expansion by nodular, irregularly shaped, pale staining areas that tend to be located nearer to the subcapsular sinus and lymph node capsule (Fig. 41.1). Lymphoid follicles are usually hyperplastic in early stages (Fig. 41.2), but are compressed and eventually become atrophic in later stages (8,9). At high-power magnification, the pale areas are composed of numerous interdigitating dendritic cells (IDCs) and Langerhans cells with small lymphocytes in the background (Fig. 41.3) (4,8,9,10). Some phagocytic histiocytes also can be present, and these cells may contain cytoplasmic lipid and appear foamy; others have cytoplasmic pigment that can be abundant (Fig. 41.4). The pigment is mostly melanin (Fig. 41.5), but hemosiderin (Fig. 41.6) is also present to a lesser extent. Melanin pigment is thought to be carried to the lymph node by histiocytes being drained from the skin.