BRIEF REPORT Free-Floating Collagen Fibers in Interstitial Mycosis Fungoides Gerardo Ferrara, MD,* Giuliana Crisman, MD,† Iris Zalaudek, MD,‡ Giuseppe Argenziano, MD,§ and Catherine M. Stefanato, MD, FRCpath¶ Abstract: We present a case of interstitial mycosis fungoides showing pseudodovascular clefts with ‘‘free-floating’’ collagen fibers surrounded by neoplastic T lymphocytes. Such a finding further expands the histopathologic spectrum of mycosis fungoides and could be taken into account in its differential diagnosis from gran- uloma annulare, inflammatory morphea, and interstitial granuloma- tous drug reaction. Key Words: interstitial mycosis fungoides, collagen fibers, immu- nohistochemistry, differential diagnosis (Am J Dermatopathol 2010;0:000–000) INTRODUCTION The concept of interstitial mycosis fungoides (IMF) was first set forth by A. Bernard Ackerman (unpublished observation quoted by Su et al 1 ) and subsequently described by Shapiro and Pinto. 2 This entity is a well-recognized histopathologic mimicker of granuloma annulare and in- flammatory morphea. 1 We herein present a case of IMF showing a novel morphologic feature, namely, the presence of pseudovascular clefts with ‘‘free-floating’’ collagen fibers within the reticular dermis. A 60-year-old white woman presented with a 10-month history of itchy erythematous and scaly lesions of the trunk and limbs (Fig. 1, top). Her history was remarkable for mild hypercholesterolemia and hyperglycemia, but she was not on medication. Two skin biopsies were taken, one from the abdomen (Fig. 1, left), and one from the thigh (Fig. 1, right). The histopathologic findings at scanning magnification were unexpectedly different between the 2 biopsies (Fig. 1, lower left and right). The first biopsy specimen (abdomen) showed a mild superficial mononuclear infiltrate with no appreciable involvement of the epidermis (Fig. 2, top left). In the reticular dermis, there was a mild to moderately dense perivascular and interstitial mononuclear infiltrate (Fig. 2, top right), often arranged around semicircular clefts with pseudovascular features; these clefts imparted a free-floating appearance to the collagen fibers, which showed no alteration in their staining properties (Fig. 2, bottom left). Histochemical stains disclosed tiny dermal deposits of mucin around some clefts (Fig. 2; bottom middle); the elastic fibers were reduced to absent between the free-floating collagen fibers (Fig. 2, bottom right). No elastophagocytosis was appreciated. Immunohistochemically (Table 1), the majority of the mono- nuclear dermal cells were CD3 + (Fig. 3, top left) CD4 + CD5 + CD7 + CD8 2 . These T lymphocytes were characteristically arranged around the clefts within the reticular dermis (Fig. 3, top right). Approximately, one-third of the dermal mono- nuclear cells were CD68 + histiocytes, mostly found in the interstitial areas with an ‘‘Indian file’’ arrangement (Fig. 3, bottom); no giant cells were detected. CD79a + B lympho- cytes were present only occasionally. The anti-CD31/ PECAM-1 and the antipodoplanin antibodies failed to stain the clefts around the free-floating collagen bundles, thus ruling out a vascular component. The biopsy from the lesion on the thigh, which was taken subsequently to the histopathologic examination of the first biopsy, showed a moderately dense and superficial lymphoid infiltrate filling the papillary dermis and associ- ated with fibrosis, (Fig. 1, bottom right). Epidermotropism with Pautrier microabscesses (Fig. 1, bottom right, arrow) and slight cytological atypia of the lymphoid cells were also observed. In this second biopsy, the interstitial infiltrate within the reticular dermis was present, but it was less prominent, and it was devoid of the pseudovascular spaces, albeit still immunohistochemically characterized by a mixture of CD3 + and CD68 + cells with a predominance of the former over the latter. The immunostaining for CD3 also highlighted areas of epidermo-pilotropism. No clonal rearrangement of the T-cell receptor-g gene rearrangement was found by the Polymerase Chain Reaction-Denaturing Gradient Gel Elec- trophoresis technique performed on both paraffin-embedded biopsy samples according to the previously described pro- cedures. 3 A diagnosis of IMF was finally established based on (1) the clinicopathologic correlation; (2) the predomi- nance of T lymphocytes within the dermal interstitial infil- trate; and (3) the presence of more typical histopathologic features of mycosis fungoides in the second biopsy specimen. From the *Anatomic Pathology Unit Gaetano Rummo General Hospital, Benevento, Italy; †Department of Dermatology, University of Trieste, Trieste, Italy; ‡Department of Dermatology, Medical University of Graz, Graz, Austria; §Department of Dermatology, Second University of Naples, Naples, Italy; and {Department of Dermatopathology, St. John’s Institute of Dermatology, St. Thomas’ Hospital, London, UK. Reprints: Gerardo Ferrara, MD, Department of Oncology, Pathologic Anatomy Unit, Gaetano Rummo General Hospital, Via dell’Angelo 1, I-82100 Benevento, Italy (e-mail: gerardo.ferrara@libero.it). Conflict of interest: none to be declared. Copyright Ó 2010 by Lippincott Williams & Wilkins Am J Dermatopathol  Volume 0, Number 0, Month 2010 www.amjdermatopathology.com | 1