Treatment-refractory cutaneous Rosai-Dorfman disease responsive to oral methotrexate and topical trametinib

Nasopharyngeal Representation of Rosai-Dorfman Disease; a Case Report

A 52-year-old female patient complaining of progressive nasal obstruction six months ago, nasopharyngoscopy revealed a nasopharyngeal large fleshy non-pulsatile mass, ear examination and tympanometry revealed left middle ear effusion without any abnormalities in mouth or oropharynx. There was no enlarged cervical lymphadenopathy in contrast to most RDD cases. Given clinical examination and radiological findings, an excisional biopsy was done under general anaesthesia with left ear ventilation T-tube insertion. Histopathological examination of the biopsy specimen reveals a unique histopathological feature, "emperipolesis", and immunohistochemistry confirmed the diagnosis of Rosai-Dorfman Disease.

Cutaneous Rosai-Dorfman disease with MAP2K1 mutation, initially mimicking an infection with parasitized histiocytes

Rarely, Rosai-Dorfman disease (RDD) manifests exclusively in the skin, typically as nodules on the trunk and extremities. Recognition of characteristic histopathologic features enables diagnosis of RDD. A 55-year-old female presented with a 7-year history of cutaneous nodules involving the trunk and extremities. A prior skin biopsy specimen at a different institution had demonstrated a dense dermal lymphohistiocytic infiltrate with histiocytes containing GMS+ forms, favored to represent cryptococcal organisms, with a differential diagnosis including other infections with parasitized histiocytes. Despite antibiotic therapy, lesions persisted. After a presentation to our institution, a biopsy specimen showed a diffuse infiltrate, including histiocytes with voluminous pale cytoplasm with focal emperipolesis of inflammatory cells and S100 immunohistochemical positivity. Clinical and radiologic examinations did not identify significant extracutaneous involvement. A genetic study performed on the biopsy specimen identified a K57Q mutation of MAP2K1. The presence of this mutation correlated with prior reports of MAP2K1 mutation in classic RDD, thereby supporting our histopathologic diagnosis of RDD over an infectious process and further illuminating options for targeted therapies. At 3-year follow-up, the patient has been managed with a course of systemic corticosteroids and excision of bothersome lesions. Consideration of systemic therapy is ongoing.

ERK hyperactivation in epidermal keratinocytes impairs intercellular adhesion and drives Grover disease pathology

Grover disease is an acquired epidermal blistering disorder in which keratinocytes lose intercellular connections. While its pathologic features are well defined, its etiology remains unclear, and there is no FDA-approved therapy. Interestingly, Grover disease was a common adverse event in clinical trials for cancer using B-RAF inhibitors, but it remained unknown how B-RAF blockade compromised skin integrity. Here, we identified ERK hyperactivation as a key driver of Grover disease pathology. We leveraged a fluorescent biosensor to confirm that the B-RAF inhibitors dabrafenib and vemurafenib paradoxically activated ERK in human keratinocytes and organotypic epidermis, disrupting cell-cell junctions and weakening epithelial integrity. Consistent with clinical data showing that concomitant MEK blockade prevents Grover disease in patients receiving B-RAF inhibitors, we found that MEK inhibition suppressed ERK and rescued cohesion of B-RAF-inhibited keratinocytes. Validating these results, we demonstrated ERK hyperactivation in patient biopsies from vemurafenib-induced Grover disease and from spontaneous Grover disease, revealing a common etiology for both. Finally, in line with our recent identification of ERK hyperactivation in Darier disease, a genetic disorder with identical pathology to Grover disease, our studies uncovered that the pathogenic mechanisms of these diseases converge on ERK signaling and support MEK inhibition as a therapeutic strategy.

ERK hyperactivation in epidermal keratinocytes impairs intercellular adhesion and drives Grover disease pathology

Grover disease is an acquired dermatologic disorder characterized by pruritic vesicular and eroded skin lesions. While its pathologic features are well-defined, including impaired cohesion of epidermal keratinocytes, the etiology of Grover disease remains unclear and it lacks any FDA-approved therapy. Interestingly, drug-induced Grover disease occurs in patients treated with B-RAF inhibitors that can paradoxically activate C-RAF and the downstream kinase MEK. We recently identified hyperactivation of MEK and ERK as key drivers of Darier disease, which is histologically identical to Grover disease, supporting our hypothesis that they share a pathogenic mechanism. To model drug-induced Grover disease, we treated human keratinocytes with clinically utilized B-RAF inhibitors dabrafenib or vemurafenib and leveraged a fluorescent biosensor to confirm they activated ERK, which disrupted intercellular junctions and compromised keratinocyte sheet integrity. Consistent with clinical data showing concomitant MEK blockade prevents Grover disease in patients receiving B-RAF inhibitors, we found that MEK inhibition suppressed excess ERK activity to rescue cohesion of B-RAF-inhibited keratinocytes. Validating these results, we demonstrated ERK hyperactivation in skin biopsies of vemurafenib-induced Grover disease, but also in spontaneous Grover disease. In sum, our data define a pathogenic role for ERK hyperactivation in Grover disease and support MEK inhibition as a therapeutic strategy.

GRAPHICAL ABSTRACT

Rosai-Dorfman Disease, Presenting as a Right Atrial Mass with Involvement of the Tricuspid Valve in a 54-Year-Old Woman

BACKGROUND Sinus histiocytosis with massive lymphadenopathy (SHML), Rosai-Dorfman disease, or Rosai-Dorfman-Destombes disease (RDD), is a rare non-Langerhans cell of unknown etiology. This report is of a case of isolated SHML, or Rosai-Dorfman disease, presenting as a right atrial mass with involvement of the tricuspid valve in a 54-year-old woman. This case shows the challenges of diagnosing this condition in the heart and the challenges of treating this rare disease with the limited information on the efficacy of the treatment modalities. CASE REPORT A 54-year-old Asian woman presented to the Emergency Department with chest and right upper quadrant pain. Transthoracic echocardiogram and computed tomography angiography showed a right atrium mass at the level of the tricuspid valve, causing moderate-severe regurgitation. Partial tumor debulking with biopsies later showed pink-yellow soft tissue, with histopathology showing histiocytes demonstrating emperipolesis. The tumor was positive for CD68 and S100 and negative for CD1a, consistent with Rosai-Dorfman disease. Subsequently the patient received targeted therapy with cobimetinib, without worsening cardiac function or disease progression. CONCLUSIONS This case highlights the challenging histopathological diagnosis of SHML, or Rosai-Dorfman disease, particularly in non-lymphoid tissue, such as the heart. Obtaining tissue for diagnosis can be challenging in this organ. Treatment is challenging when the mass cannot be extracted completely, like in our case, because other forms of therapies are not well studied and warrant further investigation, such as cobimetinib, which is a MEK pathway inhibitor approved in 2022 by the US Food and Drug Administration for histiocytic neoplasms.