Fine needle aspiration cytology of dermatopathic lymphadenitis

To delineate and describe the cytomorphologic features of dermatopathic lymphadenitis on fine needle aspirated material.

Thirteen cases of previously diagnosed dermatopathic lymphadenitis (DLN) and 10 cases of reactive lymphadenitis (RLN) (5 each of sinus histiocytosis and follicular hyperplasia) were reexamined by two independent observers. The cytologic features were semiquantitated (0-3+). Histology was available in two cases.

A variable amount of melanin pigment was seen in all 13 cases of DLN and in only 3 cases of RLN. DLN had large histiocytic collections with blood vessels at the center (12/13). The histiocytic cells had an elongated nucleus (13/13) with nuclear grooves (13/13) and pseudonucleoli (11/13). Many of these nuclei had a convoluted and crumpled appearance (11/13). On immunocytochemistry these cells were S-100 positive (six cases) and CD68 negative (one case). In contrast, in RLN with sinus histiocytosis, the histiocytes were polygonal and had rounded nuclei. Spindle-shaped histiocytes were rare, while pseudonucleoli and nuclear grooves were absent. Sinus histiocytes were CD68 positive and S-100 negative on histologic sections. Tingible body macrophages were rare (2/13) in DLN and prominent (8/10) in RLN. Mitoses were seen in DLN (6/13) and RLN (9/10).

The morphologic features found to be helpful in the diagnosis of DLN on fine needle aspiration cytology are melanin-laden macrophages with variable pigment; large, histiocytic clusters with blood vessels at the center; characteristic histiocytes, with elongated vesicular nuclei, nuclear grooves, crumpled and convoluted nuclei and pseudonucleoli; and absence of or very few tingible body macrophages. Positivity on immunostaining for S-100 and negativity for CD68 aid in the diagnosis.