SAT-094 - Pituitary Stalk Lesions: The Role of Skin Biopsy in Diagnosing Langerhans Cell Histiocytosis

Introduction:
Pituitary stalk lesions can be caused by congenital, infectious, neoplastic or inflammatory conditions. Despite extensive workup, often a final diagnosis is not achieved. Langerhans cell histiocytosis (LCH) is a rare disorder characterized by infiltration of one or more organs, including the pituitary gland, with neoplastic histiocytes. We present a case of a patient who presented with a pituitary stalk lesion who was diagnosed with LCH after developing multiorgan disease years after the initial presentation.

Case presentation:
A 32-year-old man was diagnosed with destructive thyroiditis, arginine vasopressin (AVP) deficiency and panhypopituitarism at age 26, and found to have a 6 mm pituitary stalk thickening on magnetic resonance imaging (MRI), suspicious for hypophysitis. Extensive evaluation was non-diagnostic and pituitary stalk biopsy was deferred due to the inherent risks. A computed tomography (CT) of the chest, abdomen, and pelvis revealed two 3-4mm calcified mediastinal lymph nodes and a punctate nodule in right lung. Empiric treatment with high dose steroids did not improve the pituitary stalk thickening. He continued therapy with desmopressin, prednisone, levothyroxine, and testosterone alongside yearly MRIs which remained stable. After being lost to follow up for two years, he presented with several new cutaneous findings: plaques with purulent drainage in bilateral axilla, scale on the scalp, and crusted papules and plaques on the trunk. A biopsy of the lesion on the back and immunohistochemical stains (CD1a, S100, PU.1, CD163-positive) confirmed the clinical suspicion of LCH. Next generation sequencing of the skin biopsy revealed a BRAF N486_P490del mutation. A Fluorodeoxyglucose (FDG) Positron Emission Tomography/Computed Tomography (PET/CT) showed multiple FDG avid cutaneous lesions, increased uptake in thyroid gland and multifocal cystic lesions in both lungs. The pituitary stalk lesion was stable on repeat MRI. He is currently being managed by Hematology-Oncology for his multisystem disease.

Conclusion:
The evaluation of pituitary stalk lesions is complex as tissue sampling is frequently not feasible. In adults, LCH may present with multisystemic disease, commonly with pulmonary, bone, skin, and hypothalamic-pituitary involvement. Anterior pituitary dysfunction presents in 20% of cases. AVP deficiency is the most common finding which may precede the diagnosis by years. About 30-50% of patients can present with diverse cutaneous findings including seborrheic dermatitis-like lesions, crusted or scaly papules, ulcerative plaques, and pustules with a predilection for the scalp and intertriginous areas. Skin biopsy remains a minimally invasive diagnostic tool in LCH patients with multisystem disease. Close follow up is needed as the underlying condition may not be apparent on initial evaluation as was demonstrated in our patient.

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