Cutaneous malakoplakia arising on the ankle of a patient with pyoderma gangrenosum.

Malakoplakia is a rare chronic inflammatory condition that most commonly involves the urogenital tract. Cutaneous malakoplakia is extremely rare and many patients diagnosed with skin involvement are immunosuppressed. While the clinical presentation of cutaneous malakoplakia is variable, the histopathologic features are quite distinct and include sheets of closely packed dermal histiocytes with foamy-appearing cytoplasm and Michaelis-Gutmann bodies that are positive with certain immunohistochemical stains.

Hypertrophic Lichen Planus: An Up-to-Date Review and Differential Diagnosis.

Context.—: Hypertrophic lichen planus (HLP) is a variant of lichen planus that can be difficult to diagnose based on histopathologic features alone. Thus, patient clinical history and clinicopathologic correlation are essential considerations to make the correct diagnosis.

Primary cutaneous T-cell lymphoma: a review of the most common entities with focus on recent updates.

Cutaneous T-cell lymphomas are an heterogeneous group of uncommon lymphoid neoplasms that are challenging to diagnose and require close collaboration between dermatologists, pathologists and hematologists/oncologists. This article reviews the most common cutaneous T-cell lymphomas: mycosis fungoides (both classic and variant forms) as well as its leukemic counterpart Sézary syndrome, CD30+ T-cell lymphoproliferative disorders including the ever-expanding group of lymphomatoid papulosis and primary cutaneous anaplastic large cell lymphoma, and primary cutaneous CD4+ small/medium lymphoproliferative disorder. We discuss the classic clinical and histopathologic features of these lymphomas and review how they can be distinguished from reactive entities.

Mesenchymal tumours with melanocytic expression: a potential pitfall in the differential diagnosis of malignant melanoma.

Mesenchymal tumours with melanocytic expression can pose a diagnostic challenge because they frequently demonstrate both morphological and immunohistochemical overlap with other cutaneous melanocytic neoplasms. Therefore, they present potential pathological pitfalls that may lead to a misdiagnosis of malignant melanoma. Mesenchymal neoplasms that closely mimic melanoma include malignant melanotic nerve sheath tumour (melanotic schwannoma), epithelioid schwannoma, malignant peripheral nerve sheath, cutaneous syncytial myoepithelioma, clear cell sarcoma of soft tissue, and perivascular epithelioid cell tumour.