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Immune Cells Show the Way in This Medical Mystery

A 54-year-old man presents to a foot and ankle clinic in Maryland with a diffuse, hard lesion in the middle of the arch of his left foot; it is tender to the touch and painful to walk on.

He explains that it began developing gradually about 3 years earlier as a dry, scaly spot, and that the skin later cracked but there was no pain. He says he had not been concerned, since he had a history of having severe eczema and dry patches of skin in the same spot on his foot.

However, his efforts to treat the eczema with topical cortisone cream and “over-the-counter acid” have been ineffective, he said, adding that he became concerned when the lesion slowly grew thicker and harder.

The patient’s surgical and medical histories include thyroidectomy (for thyroid cancer) at age 28, a diagnosis of bipolar disorder, headaches/migraines, and high blood pressure. His family history is unremarkable, and clinical assessment reveals no major abnormalities.

Dermatological Examination

Dermatological assessment shows a 3.0-cm, scaly, keratotic patch with slight erythema in the plantar central region of the left arch, which is notably tender to palpation. There is no evidence of skin atrophy or lymphadenopathy. Laboratory test results are within normal limits.

Clinicians perform a skin punch biopsy and send the sample for histological evaluation.

The report notes infiltration of atypical lymphocytes in the upper dermis. Most of the atypical lymphocytes are round or ovoid with a cerebriform nuclear contour but with no clear nuclear membrane or nucleoli.

Single units or small clusters of these have infiltrated up into the epithelial layers (epidermotropism), down into the eccrine sweat glands (syringotropism) and the walls of the blood vessels in the dermis.


Histopathology and immunostaining profiles of mycosis fungoides palmaris et plantaris: (A) An infiltrate of the atypical lymphocytes in the upper dermis (hematoxylin and eosin [H&E], 40×1). (B) Round or ovoid atypical lymphocytes with cerebriform nuclear contour and no clear nuclear membrane or nucleoli (HE, 400×1). (C) Atypical lymphocytes infiltrating into the epidermis (epidermotropism) (HE, 100×1). (D) Atypical lymphocytes infiltrating into eccrine sweat glands (syringotropism) (HE, 100×1). (E) Perivascular infiltration of the atypical lymphocytes in the dermis (HE, 100×1). (F) Strong CD4 expression in atypical lymphocytes (3, 3 -diaminobenzidine [DAB], 100×1). (G) Reduced CD7 expression in atypical lymphocytes (DAB, 100×1). (H) Reduced CD8 expression in atypical lymphocytes (DAB, 100×1).

Immunostaining of the atypical lymphocytes shows almost uniformly strong positive staining for CD3, CD4 antibodies and about 30% positivity for CD7 and CD8; staining for CD20 was negative.

Clinicians note an approximately 3:1 ratio of CD4- to CD8-positive cells. Results of periodic acid-Schiff staining for fungal elements are negative for both spores and hyphae; yet the histomorphology and immunostaining profiles are judged to be consistent with mycosis fungoides palmaris et plantaris (MFPP).

The team discusses the treatment options with the patient, and he is referred to a dermatologist. The patient receives topical psoralen plus ultraviolet A (PUVA) photochemotherapy, which results in complete remission.

At 5-year follow-up, the