Histiocytic neoplasms, a rare and heterogeneous group of disorders, primarily include Erdheim-Chester disease, Langerhans cell histiocytosis, and Rosai-Dorfman disease. Due to their diverse clinical manifestations, the greatest challenge posed by these neoplasms is the establishment of a diagnosis, which often leads to a delay in institution of appropriate therapy. Recent insights into their genomic architecture demonstrating mitogen-activated protein kinase/extracellular signaleregulated kinase pathway mutations have now enabled potential treatment with targeted therapies in most patients. This consensus statement represents a joint document from a multidisciplinary group of physicians at Mayo Clinic who specialize in the management of adult histiocytic neoplasms. It consists of evidence-and consensus-based recommendations on when to suspect these neoplasms and what tests to order for the diagnosis and initial evaluation. In addition, it also describes the histopathologic and individual organ manifestations of these neoplasms to help the clinicians in identifying their key features. With uniform guidelines that aid in identifying these neoplasms, we hope to improve the awareness that may lead to their timely and correct diagnosis.

Background Reactive granulomatous dermatitis (RGD) is an umbrella term used to describe interstitial granulomatous dermatitis (IGD), palisaded neutrophilic and granulomatous dermatitis (PNGD), and interstitial granulomatous drug eruption (IGDR). Objective The aim of this study was to describe systemic associations of RGD, explore possible associations between histopathologic findings and systemic RGD associations and determine clinical relevance of RGD subtypes. Methods We retrospectively studied clinical and histopathologic characteristics of patients with RGD from 1990 through 2020. Results Of 65 patients with RGD (41 women, 24 men; median age at diagnosis, 62 years), 37 had IGD, 26 had PNGD, and 2 had IGDR. Fifty patients (76.9%) had an associated systemic condition; rheumatologic conditions were identified for 34 (52.3%) patients. The associated systemic condition occurred before RGD in approximately 75% of patients. Statistical analyses did not show significant associations between specific subtypes of RGD and systemic diseases or treatment response, and specific histopathologic findings were not predictive of an associated systemic disease. Conclusions Although most patients with RGD had an associated systemic condition, subtypes of RGD did not correlate with systemic associations, lending support to the use of the umbrella term RGD.

Background Few large studies have assessed spironolactone treatment of adult female acne. Objectives To explore the role of spironolactone in the treatment of adult female acne. Methods We performed a retrospective case series assessing the efficacy of spironolactone treatment of a cohort of women evaluated at Mayo Clinic in Rochester, Minnesota, from 2007 through 2017. Results In total, 395 patients (median age, 32 years) received a median spironolactone dose of 100 mg daily. Approximately two‐thirds of patients (66.1%) had a complete response; 85.1% had a complete response or a partial response greater than 50%. Median times to initial response and maximum response were 3 and 5 months. Efficacy was observed across all severity subtypes of acne, including those with papulopustular and nodulocystic acne. Patients received long‐term treatment with spironolactone (median duration, 13 months) and had few adverse effects. Conclusions Spironolactone is a safe and effective treatment of acne for women.

Cutaneous reactions from targeted biologics are increasingly common. We describe a case of a cutaneous lichenoid drug eruption from the RANK inhibitor denosumab and a previously unreported lymphohistiocytic reaction pattern. The clinical and histopathological details of this case will aid in recognition, diagnosis, and treatment of drug rashes from denosumab.

Summary Background Wet dressings combined with topical corticosteroids are beneficial for patients with generalized and refractory dermatosis; however, to our knowledge, serum levels after topical corticosteroid absorption during intensive therapy have not been reported previously. Aim To examine serum levels of triamcinolone acetonide (TAC) after topical corticosteroid application during intensive wet‐dressing therapy. Methods We performed a retrospective study of adult patients admitted for inpatient wet‐dressing therapy from 7 November 2015 to 24 June 2016. Data were collected on sex, age, body surface area, TAC serum levels, number of wet‐dressing changes after 24 and 48 h, and type of wet dressing. Results In total, 29 patients (14 men, 15 women) were assessed. Median [interquartile range (IQR)] age was 57 years (51.5–67.0 years) and involved body surface area was 1.98 m2 (1.88–2.15) m2. Before the 24‐hour blood draw, patients had received 1–3 dressing changes. Median (IQR) TAC level at 24 h was 0.33 µg/dL (0.20–0.58 µg/dL), with no significant difference noted between the number of dressing changes and TAC serum level. At 48 h, results of a serum TAC test were available for 22 patients with 2–6 dressing changes. Mean (IQR) serum level was 0.30 µg/dL (0.30–0.87 µg/dL). For each additional dressing change, there was an estimated 0.21 µg/dL increase in TAC serum level (95% CI 0.11–0.31; P < 0.001). TAC serum level was not significantly associated with sex, age, body surface area or dressing type. Conclusions Intensive, inpatient wet‐dressing therapy is associated with detectable TAC serum levels. However, we suspect that topical TAC has a primarily local therapeutic effect on the skin.