Pathologic basis of pyogenic, nonpyogenic, and other spondylitis and discitis.

Pyogenic spondylitis and discitis are usually seen following a recent infection or surgery. A septic embolus causes an infarcted area within the bone. Pyogenic spondylitis is characterized by edema, vascular leakage, and supportive inflammatory reaction characterized with polymorphonuclear leukocytes. In tuberculosis of the spine, active lesions are characterized by formation of epithelioid granulomas with central caseating necrosis. Mycobacterium tuberculosis can be shown by histochemical stains for acid-fast bacteria or by immunochemistry. In brucella spondylitis, microgranulomatous proliferation composed of histiocytes containing numerous bacilli without caseating necrosis is characteristic. Brucella melitensis can be shown on histochemical Gram stain.