Crystal-Storing Histiocytosis of the Stomach: An Unusual Clinical Context of a Rare Entity

Crystal-storing histiocytosis (CSH) is a rare entity pathologically defined by the presence of eosinophilic histiocytes filled with refractile crystalline structures, which are most often IgG kappa monoclonal immunoglobulins. Though CSH is a benign lesion, it is often associated with a concurrent or developing lymphoproliferative disorder. Literature review reveals kidneys, lungs, lymph nodes, bone marrow, skin, and eyes as the most common presentation sites, with the stomach as the most common gastrointestinal (GI) site. Reports of CSH in the GI setting have noted simultaneous infections with <i>Helicobacter pylori</i> and a range of associated lymphomas. We report a lesion from the stomach of a 45-year-old woman endoscopically described as containing patchy atrophic and nodular mucosa, biopsied for gastric mapping due to a reported history of atrophic gastritis without confirmatory serologic antibodies. Immunohistochemical stains highlighted CD68 positive, keratin negative, cells with cytoplasmic kappa positivity. The smooth muscle actin marker highlighted rare smooth muscle fibers. CSH was diagnosed in a background of chronic inactive gastritis without evidence of <i>Helicobacter pylori</i> or associated extranodal marginal zone lymphoma. Though rare in the GI tract, it is important to recognize this entity and its potential to occur concurrently with lymphoproliferative disorders, inflammatory conditions, and possible autoimmune diseases.