title: A challenging diagnosis: crystal-storing histiocytosis in plasma cell myeloma.
abstract: OBJECTIVE
  Crystal-storing histiocytosis (CSH) is an uncommon finding in plasma cell neoplasms. CSH is thought to be an intralysosomal deposition of secreted paraproteins or immunoglobulins, which usually express κ immunoglobulin light chains that finally aggregate in crystals. Because of its rarity, CSH in bone marrow often makes diagnosis difficult.
  
  
  METHODS
  A 57-year-old woman had IgA κ monoclonal proteinemia and monoclonal proteinuria. In the bone marrow aspirate, plasma cells were initially counted less than what would be expected, whereas histiocytes with intracellular crystals were increased. Then, we used α-naphthyl acetate esterase (ANAE) staining to distinguish between true histiocytes and plasma cells. Immunostaining for κ, CD138, CD56, and CD68 was performed on a bone marrow biopsy specimen.
  
  
  RESULTS
  True histiocytes containing crystalline inclusions were stained strongly for ANAE, while unstained cells with intracytoplasmic crystals represented plasma cells. The biopsy specimen revealed diffuse infiltration of CD138-positive plasma cells. We also confirmed the presence of plasma cells, histiocytes, and their crystallized inclusions with the immunostaining. The patient was finally diagnosed with plasma cell myeloma.
  
  
  CONCLUSIONS
  The diagnosis was challenging; the bone marrow findings resembled features of other histiocytic disorders. The use of immunohistochemistry enabled the diagnosis of CSH in the presence of plasma cell myeloma.
authors.affiliation: From the Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea;
authors.forename: Jee-Soo
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea;
authors.forename: Kyongok
authors.initials: K
authors.lastname: Im
authors.affiliation: Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea;
authors.forename: Si Nae
authors.initials: SN
authors.lastname: Park
authors.affiliation: From the Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea;
authors.forename: Hee Sue
authors.initials: HS
authors.lastname: Park
authors.affiliation: From the Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea;
authors.forename: Jung-Ah
authors.initials: JA
authors.lastname: Kim
authors.affiliation: From the Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea;
authors.forename: Qute
authors.initials: Q
authors.lastname: Choi
authors.affiliation: From the Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea;
authors.forename: Seon Young
authors.initials: SY
authors.lastname: Kim
authors.affiliation: Department of Laboratory Medicine, Gang Neung Asan Hospital, Gangwon-do, Republic of Korea;
authors.forename: Choong-Hwan
authors.initials: CH
authors.lastname: Cha
authors.affiliation: Department of Internal Medicine, Gang Neung Asan Hospital, Gangwon-do, Republic of Korea; and.
authors.forename: Ho-Suk
authors.initials: HS
authors.lastname: Oh
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea.
authors.forename: In Ho
authors.initials: IH
authors.lastname: Kim
authors.affiliation: From the Department of Laboratory Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea; Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea; soonlee@plaza.snu.ac.kr.
authors.forename: Dong Soon
authors.initials: DS
authors.lastname: Lee
mesh_terms: D005260:Female; D015614:Histiocytosis / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D002479:Inclusion Bodies / Q000473:pathology; D008875:Middle Aged; D009101:Multiple Myeloma / Q000473:pathology*
keywords: Crystal-storing histiocyte; Crystalline inclusion; Plasma cell myeloma