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Erdheim–Chester disease (ECD) is a rare, non‐Langerhans histiocytic disease, with the manifestation of cutaneous lesions becoming further recognised and understood. Most commonly presenting with xanthelasma‐like lesions, cutaneous manifestations are the first noticeable sign of ECD in a significant number of patients. Other commonly reported cutaneous lesions of ECD include panniculitis‐like lesions and granuloma annulare‐like lesions. While previously reported papular lesions of ECD include crusty yellow and erythematous papules, small, pink to fleshy coloured papules, and verruca plana‐like papules, papulonodular eruptions consistent with fibrous histiocytomas are a rare and underreported sequala of ECD. Here, we report an 86‐year‐old male with a history of prostate and bladder cancer who presented with eruptive fibrous histiocytomas, prompting workup that lead to a diagnosis of ECD. The patient received expedited imaging given the rare association of eruptive fibrohistiocytic lesions with malignancy, revealing diffuse perinephric and urothelial soft tissue thickening and enhancement, which was biopsied and found to harbour the BRAF V600E mutation. One could reasonably hypothesise that the pathologic mechanism occurring in the perinephric and urothelial soft tissue areas of this patient bodes similarities to the cutaneous sites consistent with the fibrohistiocytic lesions. This may present a potential clue to the poorly understood origin and pathogenesis of ECD. We present a rare case of ECD due to the cutaneous finding of diffusely distributed monomorphic eruptive fibrous histiocytomas. Advancements in the understanding of pathogenesis and therapeutics makes early diagnosis of ECD paramount, but more work must be done in understanding its etiology and pathogenesis.

To the Editor: Polyomavirus type BK nephropathy is an aggressively destructive disease occurring in up to 8 percent of patients with renal allografts, 1 , 2 with rates of graft loss within one year of 30 to 65 percent. 3 , 4 There is no therapy with proven efficacy. Leflunomide (Arava), approved for the treatment of rheumatoid arthritis, is an immunosuppressive drug, yet its active metabolite, A77 1726, has substantial antiviral activity in vitro and in animals. 5 From July 2001 to April 2004, we used leflunomide as the initial antiviral therapy in 17 patients with biopsy-proven BK nephropathy. All but one of these patients . . .

Post-infectious glomerulonephritis (PIGN) is an immune complex-mediated glomerular injury that typically resolves. Dominant C3 deposition is characteristic of PIGN, but with the emergence of C3 glomerulonephritis (C3GN) as a distinct entity, it is unclear how the pathologic similarities between PIGN and C3GN should be reconciled. Therefore, nephrologists and nephropathologists need additional guidance at the time of biopsy.MethodsWe studied 23 pediatric and young adult patients diagnosed with PIGN. Patients were divided into two groups, one with co-dominance between C3 and immunoglobulins and the other meeting proposed diagnostic criteria for C3GN. Clinical and pathological features were compared.ResultsNo clinical and/or pathological features could distinguish between those with C3-co-dominant deposits and those with C3 dominance. Nearly all patients in both groups regained their baseline renal function without clinical intervention.ConclusionsAlthough the identification of abnormalities of the alternative pathway of complement is characteristic of C3GN, testing is not widely available and the turnaround time often exceeds 1 month. Our study found that PIGN with either co-dominant or dominant C3 deposition in a cohort of young patients has excellent short-term outcomes. Close clinical observation for persistent abnormalities, such as hypocomplementemia, prolonged hematuria or proteinuria, is recommended to single out patients that may harbor intrinsic complement abnormalities.

Background Malignant angiomyolipoma is an uncommon tumor of the class of perivasciular epithelioid cell neoplasms (PEComas). These tumors are characteristically driven by deleterious mutations in the tumor suppressors TSC1 and TSC2 , whose gene products typically act to inhibit mTOR. There are several cases of malignant angiomyolipoma which exhibit transient responses to mTOR inhibitors, forming the basis of current practice guidelines in malignant PEComa. However the tumors ultimately acquire resistance, and there is no well-established second-line option. Despite the increasing prevalence of immunotherapy across a wide range of solid tumors, little is known about the immune infiltrate and PD-L1 expression of angiomyolipoma. Furthermore, there is no reported case on the treatment of malignant angiomyolipoma with an immune checkpoint inhibitor. Case presentation A 38 year-old man presented with gross hematuria and was diagnosed with renal epithelioid angiomyolipoma. Despite surgical resection, the tumor recurred and metastasized. Targeted genomic sequencing revealed a deleterious mutation in TSC2 , and the patient was treated with the mTOR inihbitor everolimus. The patient went on to have a partial response but ultimately progressed. He was then treated with the anti-PD-1 immune checkpoint inhibitor nivolumab, and achieved a durable near-complete response which is ongoing after two years of treatment. Immunohistochemical staining of tumor tissue revealed strong PD-L1 expression and a brisk T-cell infiltrate. Conclusions We report on the first durable systemic treatment of malignant epithelioid angiomyolipoima with the use of PD-1 antibody nivolumab. Given the absence of prospective clinical trials in this exceedingly rare disease, particularly in the second-line setting, immune checkpoint inhibitors like nivolumab should be considered.

Abstract Although drug reaction with eosinophilia and systemic symptoms (DRESS) is associated with antiretrovirals, there are no published reports of bictegravir-induced DRESS. Bictegravir is recommended as first-line treatment for patients with human immunodeficiency virus (HIV). Recognition of DRESS, its skin manifestations, and potential complications is vital for appropriate care and management of acute HIV.

The Columbia working classification of focal segmental glomerulosclerosis (FSGS) identifies five types of glomerular lesions, designated collapsing (COLL), cellular (CELL), glomerular tip lesion (GTL), perihilar (PH), and not otherwise specified (NOS) variant lesions. FSGS COLL and non-collapsing variants of FSGS are described in human immunodeficiency virus (HIV)-associated kidney disease. This study examined the range and relationships of Columbia-type segmental sclerosing lesions in biopsies from patients with HIV infection. We identified 47 renal biopsies from 46 patients with HIV infection obtained over an 8-year period. Twenty-seven biopsies from 26 patients had FSGS. Sixteen biopsies had FSGS COLL (59.3%), 3 had CELL (11.1%), 5 had NOS (18.5%), 2 had PH (7.4%), and 1 had GTL (3.7%) by the Columbia classification. Biopsies had more than one type of Columbia FSGS lesion in 63% and one type in 37%. Single types of FSGS lesions were identified in eight of eight biopsies with ≤10 glomeruli. Combinations of lesions were observed in 17 of 19 (89.5%) with >10 glomeruli, and the coincidence of COLL, CELL, and NOS lesions was not random. NOS, COLL, and CELL morphologic lesions of FSGS frequently coexist in kidney biopsies from HIV+ patients. Combined patterns of FSGS suggest that lesions identified by Columbia criteria may be part of a spectrum of responses to injury in the setting of HIV infection.