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Background Sclerosing mesenteritis (SM) is sometimes used as an umbrella-term for idiopathic inflammatory conditions in the mesentery. Mesenteric panniculitis (MP) is a radiological finding and its relation to clinical SM is not fully understood. The aims of this study were to determine whether any correlation could be found between the radiological findings and the clinical disease course. Methods Patients observed due to idiopathic inflammation of the mesentery were identified. If SM could be verified histologically or MP radiologically, the patients were included in this descriptive retro perspective study. Results Typical radiological changes were observed in 27 patients. A majority (23/27) of these patients had mild to moderate symptoms. This group with typical radiology was labelled MP. Four patients were included due to histologically verified disease but had uncharacteristic radiology involving multiple compartments of the abdomen. All four had marked systemic inflammation, fever and fluctuating radiologic findings. Three had severe disease with multiple hospitalisations and complications but responded promptly to corticosteroids. This group was denoted SM. Conclusions We have identified two subgroups of patients; firstly, MP with stable and characteristic radiologic changes and secondly SM with atypical radiology and a more aggressive clinical course. We propose that the term SM should be reserved for this latter condition.

Subcutaneous panniculitis-like T cell lymphoma (SPTCL), a non-Hodgkin lymphoma, can be associated with hemophagocytic lymphohistiocytosis (HLH), a life-threatening immune activation that adversely affects survival 1 , 2 . T cell immunoglobulin mucin 3 (TIM-3) is a modulator of immune responses expressed on subgroups of T and innate immune cells. We identify in ~60% of SPTCL cases germline, loss-of-function, missense variants altering highly conserved residues of TIM-3, c.245A>G (p.Tyr82Cys) and c.291A>G (p.Ile97Met), each with specific geographic distribution. The variant encoding p.Tyr82Cys TIM-3 occurs on a potential founder chromosome in patients with East Asian and Polynesian ancestry, while p.Ile97Met TIM-3 occurs in patients with European ancestry. Both variants induce protein misfolding and abrogate TIM-3’s plasma membrane expression, leading to persistent immune activation and increased production of inflammatory cytokines, including tumor necrosis factor-α and interleukin-1β, promoting HLH and SPTCL. Our findings highlight HLH–SPTCL as a new genetic entity and identify mutations causing TIM-3 alterations as a causative genetic defect in SPTCL. While HLH–SPTCL patients with mutant TIM-3 benefit from immunomodulation, therapeutic repression of the TIM-3 checkpoint may have adverse consequences. This study finds germline loss-of-function mutations in HAVCR2 , which encodes the immune modulator TIM-3, in individuals with subcutaneous panniculitis-like T cell lymphomas and hemophagocytic lymphohistiocytosis, a life-threatening inflammatory condition.

The panniculitides remain as one of the most challenging areas for clinicians, as they comprise a heterogeneous group of inflammatory diseases involving the subcutaneous fat with potentially-shared clinical and histopathological features. Clinically, most panniculitides present as red edematous nodules or plaques. Therefore, in addition to a detailed clinical history, a large scalpel biopsy of a recent-stage lesion with adequate representation of the subcutaneous tissue is essential to specific diagnosis and appropriate clinical management. Herein we review the panniculitides of particular interest to the rheumatologist.

The diagnosis of panniculitis is a relatively rare occurrence for many practising pathologists. The smaller subset of lymphocyte-predominant panniculitis is further complicated by the diagnostic consideration of T cell lymphoma involving the subcutaneous tissue, mimicking inflammatory causes of panniculitis. Accurate classification of the panniculitis is crucial to direct clinical management as treatment options may vary from non-medical therapy to immunosuppressive agents to aggressive chemotherapy. Many diseases show significant overlap in clinical and histological features, making the process of determining a specific diagnosis very challenging. However, with an adequate biopsy including skin and deep subcutaneous tissue, a collaborative effort between clinician and pathologist can often lead to a specific diagnosis. This review provides an algorithmic approach to the diagnosis of lymphocyte-predominant panniculitis, including entities of septal-predominant pattern panniculitis (erythema nodosum, deep necrobiosis lipoidica, morphea profunda and sclerosing panniculitis) and lobular-predominant pattern panniculitis (lupus erythematous panniculitis/lupus profundus, subcutaneous panniculitis-like T cell lymphoma, cutaneous γ-δ T cell lymphoma, Borrelia infection and cold panniculitis).

We report an infant with anticardiolipin (aCL) antibodies who presented with erythematous nodular skin lesions and elevated liver enzyme levels. The cutaneous manifestation was histologically lymphocytic lobular panniculitis with vasculitic and hemorrhagic changes. The infant also had low levels of anti-double stranded DNA (dsDNA) and anti-single stranded DNA (ssDNA) antibodies. There were no detectable antibodies to small nuclear ribonucleoproteins including Ro/SSA and La/SSB. His mother was consistently seronegative for any of these antibodies. Without corticosteroid therapy, cutaneous lesions resolved and anticardiolipin antibodies, but not anti-dsDNA and ssDNA antibodies, normalized within 16 months after the onset of the disease. Our patient demonstrated an uncommon presentation of aCL related cutaneous manifestation, the presentation with panniculitis being only the third such patient reported in the literature. Of great interest was the appearance of aCL antibodies and skin lesions during very early infancy.

A 20-year-old Japanese man developed generalized, subcutaneous, painless nodules, fever, abnormal liver function, serosal effusions, hepatosplenomegaly, lymphadenopathy and anemia. Skin biopsies revealed lobular panniculitis with a morphologically benign histiocytic infiltration and prominent phagocytosis. Atypical T lymphocytes were also present in the skin and liver. The diagnosis given was aggressive cytophagic histiocytic panniculitis (CHP) or aggressive subcutaneous panniculitic T cell lymphoma (SPTCL). He received cyclophosphamide, doxorubicin, and vincristine on day 1, prednisolone on days 1-5, and etoposide on days 1, 3 and 5 (CHOP-E), with the support of granulocyte colony-stimulating factor. This regimen was repeated every 2 weeks and complete clinical remission (CCR) was attained after three cycles of CHOP-E. As the clinical course of aggressive CHP is recurrent and often fatal, he was given high-dose chemotherapy followed by autologous peripheral blood stem cell transplantation (APBSCT), after five cycles of CHOP-E. He has remained in CCR for 12 months after APBSCT. High-dose chemotherapy followed by APBSCT is considered to be one of the most beneficial therapies for patients with aggressive CHP and aggressive phase SPTCL.

A young pregnant woman in her 20s presented with a 2 month history of high-grade intermittent fever. She exhibited multiple painful nodules scattered across her body for 2 months, initially small but progressively increasing in size. Initially diagnosed with Sweet syndrome, a skin biopsy revealed subcutaneous panniculitis-like T-cell lymphoma, confirmed through immunohistochemistry analysis. Treatment started with antibiotics and antipyretics. Upon ruling out septicaemia, steroid therapy was initiated, resulting in an immediate reduction in fever and rash. However, 2 months post-diagnosis, new lesions emerged, prompting a trial of dapsone, which led to their complete resolution without residual evidence. Subsequently, the case was transitioned to the obstetrician for safe management during parturition. Postpartum imaging unveiled multiple subcutaneous thickenings in the anterior and posterior abdominal walls, anterolateral portion of the right thigh and left perineal regions. After delivery, she was referred to medical oncology due to the emergence of new lesions.

Endometrial cancer (EC) is one of the most common malignancies of the female reproductive organs. The most characteristic feature of EC is the frequent association with metabolic disorders. However, the components of these disorders that are involved in carcinogenesis remain unclear. Accumulating epidemiological studies have clearly revealed that hyperinsulinemia, which accompanies these disorders, plays central roles in the development of EC via the insulin-phosphoinositide 3 kinase (PI3K) signaling pathway as a metabolic driver. Recent comprehensive genomic analyses showed that over 90% of ECs have genomic alterations in this pathway, resulting in enhanced insulin signaling and production of optimal tumor microenvironments (TMEs). Targeting PI3K signaling is therefore an attractive treatment strategy. Several clinical trials for recurrent or advanced ECs have been attempted using PI3K-serine/threonine kinase (AKT) inhibitors. However, these agents exhibited far lower efficacy than expected, possibly due to activation of alternative pathways that compensate for the PIK3-AKT pathway and allow tumor growth, or due to adaptive mechanisms including the insulin feedback pathway that limits the efficacy of agents. Overcoming these responses with careful management of insulin levels is key to successful treatment. Further interest in specific TMEs via the insulin PI3K-pathway in obese women will provide insight into not only novel therapeutic strategies but also preventive strategies against EC.

Primary cutaneous acral CD8+ T-cell lymphoma is a new provisional entity in the 2016 revision of the World Health Organization classification of lymphoid neoplasms. This is a challenging diagnosis because of its rarity, as well as its morphologic and immunophenotypic overlap with other CD8+ cytotoxic lymphoid proliferations. Appropriate classification of this entity is crucial because of its indolent clinical behavior compared with other CD8+ T-cell lymphomas. Knowledge of the clinical setting, sites of involvement, and morphologic features can aid in correct diagnosis. Here, we review the clinical and pathologic features of primary cutaneous acral CD8+ T-cell lymphoma with an emphasis on the differential diagnosis among other C8+ T-cell lymphomas.

Correspondence to Dr Uma Sundram, Department of Anatomic Pathology, Oakland University William Beaumont School of Medicine, William Beaumont Hospital, 3601 West Thirteen Mile Road, Royal Oak, MI 48073, USA; usundram@gmail.com Clinical question A 38-year-old female presents to the dermatology clinic with the complaint of barely visible ‘lumps’ on the upper arms and anterior chest wall. The tumour cells show an alpha-beta (αβ) T cell phenotype by immunohistochemistry or flow cytometry, are CD8 positive, and contain cytotoxic molecules such as granzyme B, perforin and T cell intracellular antigen-1. The neoplastic cells are Epstein-Barr virus (EBV) negative and demonstrate a T cell receptor (TCR) gene rearrangement.5 The main differential diagnostic considerations include cutaneous natural killer cell (NK)/T cell lymphoma, cutaneous gamma-delta (γδ) T cell lymphoma and lupus panniculitis.