Malignancies that can result in a pseudo-panniculitis:
(1) poorly differentiated adenocarcinoma
(2) peripheral T-cell lymphoma (especially subcutaneous T-cell lymphoma)
(3) non-T-cell lymphomas
(4) multiple myeloma
(5) leukemia
Clinical features:
(1) history or evidence of malignancy
(2) presence of systemic symptoms such as weight loss, fever and night sweats
(3) some patients will lack lymphadenopathy
(4) plaques or nodules that may be localized or diffuse
Histologic features:
(1) monotonous cell population (which may be obscured by a secondary inflammatory reaction)
(2) cytologic atypia
(3) increased mitotic activity
(4) lymphangitic and/or perineural spread
(5) infiltration between collagen bundles in the dermis
(6) little change in the connective tissue despite a dense cellular infiltrate
Immunoperoxidase stains (cytokeratin for adenocarcinoma, lymphoid markers in hematologic malignancies) can help distinguish the malignant cells. Flow cytometry can be helpful if a hematologic malignancy is suspected.
Differential diagnosis:
(1) infectious panniculitis or cellulitis
