514 DISEASES/DISORDERS
May produce false-positive results owing to cross-reactions with nontuberculous
mycobacteria.
Radiography
Thoracic, abdominal, or skeletal lesions: suggest granulomatous infectious disease.
No specific lesions for the mycobacterioses.
Pulmonary tuberculosis lesions: may become calcified or cavitated.
Cytology/Histopathology
Based on histopathologic and microbiologic evaluation of biopsy material from
affected tissue.
Aspiration of purulent material from any site after disinfection of overlying skin may
be used for microbiological identification; ultrasound-guided aspiration techniques
may be warranted. Biopsy specimens should incorporate the center of a granulomatous focus:
Tuberculosis: nodular to diffuse pyogranulomatous dermatitis with acid-fast
bacilli
Feline leprosy syndrome: lepromatous form – epithelioid macrophages withlarge numbers of acid-fast bacilli; tuberculoid form – inflammatory cells sur-
rounding necrotic foci with few acid-fast bacilli
Canine leproid granuloma: pyogranulomatous dermatitis with epithelioidmacrophages; highly variable number of organisms
Systemic nontuberculous mycobacteriosis: nodular to diffuse pyogranulomatousdermatitis and panniculitis with a paucity of organisms.
Cytology from infected tissues: with routine stains, negatively stained bacilli appear as
“ghost rods” within macrophages; in positive stains including Ziehl–Neelson: acid-
fast bacilli take up carbolfuchsin to appear pink; swabs or aspirations of draining
cutaneous lesions or lymph nodes, transtracheal wash; endoscopic brushings; rectal
cytology; impressions taken at surgical biopsy; heat-fixed samples should be submit-
ted along with tissue for culture.Culture
Culture: special media and techniques required; referral to specialized laboratories
may be required for no-tuberculous organisms (Mycobacterium.Mycology Referral,
University of Texas Health Center at Tyler, Microbiology Section).Special Testing (PCR)
PCR methodologies: useful for any of the mycobacterial infections using tissue spec-
imens or fluids; for canine leproid granuloma and the two feline leprosy syndromes
the primers are not commercially available, but can be used to identify the suspect
organisms.