Mycobacterial Spindle Cell Pseudotumor



Mycobacterial Spindle Cell Pseudotumor


Tariq Muzzafar, MBBS





Key Facts


Clinical Issues



  • Rare entity; predominantly in young men


  • History of immunosuppression and HIV infection


Microscopic Pathology



  • Spindle cells arranged in fascicles and storiform arrays with eosinophilic to granular cytoplasm


  • Clusters of epithelioid histiocytic cells with similar cytoplasmic features


  • Acid-fast stain shows numerous bacilli within spindled and epithelioid cells


  • CD68(+), lysozyme(+), vimentin(+)


  • CD31(-), CD34(-)


Ancillary Tests



  • Culture essential for confirmation


Top Differential Diagnoses



  • Kaposi sarcoma



    • Slit-like spaces with erythrocyte extravasation


    • Cytoplasmic eosinophilic globules


    • Presence of mitoses


    • Human herpes virus 8(+)


    • CD31(+), CD34(+)


  • Palisaded myofibroblastoma



    • Amianthoid fibers, scattered hemorrhagic foci, pseudocapsule


    • Smooth muscle actin(+), myosin(+), vimentin(+)


  • Inflammatory pseudotumor of lymph node



    • Hilum, trabeculae, and capsule of lymph node


    • Abundant lymphocytes, plasma cells, neutrophils


    • Vascular proliferation, flattened endothelial cells







Mycobacterial spindle cell pseudotumor involving lymph node. Fascicles and storiform arrays of spindle cells efface nodal architecture.






Mycobacterial spindle cell pseudotumor involving lymph node. Fascicles of spindle cells and scattered small lymphocytes are present. Note bland-appearing nuclei and eosinophilic granularity of cytoplasm.


TERMINOLOGY


Definitions



  • Tumor-like lesion composed of elongated spindle cells infected by Mycobacterium avium-intracellulare (MAI)


ETIOLOGY/PATHOGENESIS


Infectious Agents



  • Mycobacterium avium–intracellulare


  • Cause of distinctive tumor-like appearance is unknown


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Rare entity; ˜ 20 cases reported in literature


    • Occur in immunocompromised patients



      • Particularly in those with acquired immunodeficiency syndrome (AIDS)


  • Age



    • Predominantly affects young individuals


  • Gender



    • Predominantly affects males


Site



  • Lymph nodes most common


  • Other sites: Spleen, skin, bone marrow, lung, and brain


Laboratory Tests



  • Traditional media



    • Lowenstein-Jensen media


    • Agar-based Middlebrook medium


    • Growth of organisms is slow



      • Visible colony growth can take up to 6 weeks


  • Liquid media (growth takes ˜ 2 weeks)



    • BACTEC


    • Mycobacteria growth indicator tubes


Treatment



  • Drugs



    • HIV(+): Clarithromycin or azithromycin + ethambutol


    • HIV(-): Clarithromycin or azithromycin plus rifampin or rifabutin and ethambutol


Prognosis



  • Anti-MAI drugs are effective, particularly if immunosuppression can be reversed


IMAGE FINDINGS


Radiographic Findings



  • Lymphadenopathy


MICROSCOPIC PATHOLOGY


Histologic Features



  • Lymph node architecture effaced by elongated spindle cells (histiocytes)



    • Arranged in short fascicles and storiform arrays


  • Histiocytes have bland nuclei, eosinophilic to granular cytoplasm


  • Admixed small lymphocytes


  • No significant mitotic activity


  • Acid-fast (Ziehl-Neelsen) stain demonstrates numerous bacilli within cells


Cytologic Features



  • In Wright-Giemsa touch imprints



    • Bland histiocytes


    • Negative outlines of MAI bacilli in cytoplasm

Tags:
Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Mycobacterial Spindle Cell Pseudotumor

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