The clinical signs and diagnosis of feline atypical mycobacterial panniculitis - Veterinary Medicine
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The clinical signs and diagnosis of feline atypical mycobacterial panniculitis
Cases of AMP are infrequent, but can be exasperating. Some affected cats have skin lesions lasting months to years, despite multiple antimicrobial courses. This article tells you when to suspect AMP and how to confirm a diagnosis.


VETERINARY MEDICINE


New adjunct tests

Several new diagnostic techniques allow for more accurate diagnosis of specific variants of mycobacteria infecting cats with AMP. These techniques can be performed on biopsy samples and can be used as adjuncts to the routine diagnostic procedures previously recommended since many mycobacterial species are not easily differentiated by existing morphologic and microbiologic methods. Genetic tests, such as sequencing procedures in which the genetic code of a targeted mycobacterial gene (i.e. 16S rDNA) is identified and compared with a known database, allow identification of the specific mycobacterial species known to cause AMP.3,14 In addition, since the mycobacterial species causing AMP are difficult to identify by histologic examination, procedures such as polymerase chain reaction can demonstrate and amplify mycobacterial nucleic acid in tissue samples, which can then be used for further diagnostic testing, including sequence analysis.3,14 In one study, immunostaining with polyclonal anti-Mycobacterium bovis antibodies in skin biopsy samples from animals suspected of having AMP facilitated identification of mycobacteria when compared with conventional histochemical stains alone.15 Practitioners should inquire about the availability and cost of these new ancillary procedures from their pathology service.

Conclusion

Cats with chronic nodular dermatitis and panniculitis pose unique diagnostic problems depending on the ultimate diagnosis, but the following guidelines should prove useful for identifying most cases of AMP.

1. Determine that the cat's illness is consistent with one or more of the historical, clinical, or clinicopathologic syndromes characteristic of atypical mycobacterial infections.

2. Exclude more common causes of dermatologic disease by using routine diagnostic methods.

3. Obtain multiple deep tissue biopsy samples early in the clinical course of disease for cytologic, histologic, and microbiologic examination.

4. Alert the diagnostic laboratory receiving aspirate and biopsy samples to the possibility of an atypical mycobacterial infection, so the laboratory can apply techniques to facilitate mycobacterial species identification.

5. Request antimicrobial susceptibility testing on all successfully cultured and suspected pathogenic mycobacteria.

6. Perform serial biopsies when necessary to confirm a diagnosis of AMP.

John H. Rossmeisl Jr., DVM, MS, DACVIM (internal medicine and neurology)
Thomas O. Manning, DVM, MS, DACVD
Department of Small Animal Clinical Sciences
Virginia-Maryland Regional College of Veterinary Medicine
Virginia Tech
Blacksburg, VA 24061

REFERENCES

1. Lemarie, S.L.: Mycobacterial dermatitis. Vet. Clin. North Am. (Small Anim. Pract.) 29 (6):1291-1301; 1999.

2. Malik, R. et al.: Infection of the subcutis and skin of cats with rapidly growing mycobacteria: A review of microbiological and clinical findings. J. Feline Med. Surg. 2 (1):35-48; 2000.

3. Appleyard, G.D.; Clark, E.G.: Histologic and genotypic characterization of a novel Mycobacterium species found in three cats. J. Clin. Microbiol. 40 (7):2425-2430; 2002.

4. Alander-Damsten, Y.K. et al.: Panniculitis, due to Mycobacterium smegmatis, in two Finnish cats. J. Feline Med. Surg. 5 (1):19-26; 2003.

5. Studdert, V.P.; Hughes, K.L.: Treatment of opportunistic mycobacterial infections with enrofloxacin in cats. JAVMA 201 (9):1388-1390; 1992.

6. Malik, R. et al.: Diagnosis and treatment of pyo-granulomatous panniculitis due to Mycobacterium smegmatis in cats. J. Small Anim. Pract. 35:524-530; 1994.

7. Wilkinson, G.T. et al.: Pyogranulomatous panniculitis in cats due to Mycobacterium smegmatis. Aust. Vet. J. 58 (2):77-78; 1982.

8. Hagan, W.A.; Levine, P.: The pathogenicity of saprophytic acid-fast bacilli. JAVMA 81:723-733; 1932.

9. Kunkle, G.A. et al.: Rapidly-growing mycobacteria as a cause of cutaneous granulomas: Report of five cases. JAAHA 19:513-521; 1983.

10. Mealey, K.L. et al.: Hypercalcemia associated with granulomatous disease in a cat. JAVMA 215 (7):959-962; 1999.

11. Holick, M.F.: Defects in the synthesis and metabolism of vitamin D. Exp. Clin. Endocrinol. Diabetes 103 (4):219-227; 1995.

12. Hautmann, G.; Lotti, T.: Atypical mycobacterial infections of the skin. Dermatol. Clin. 12 (4):657-668; 1994.

13. Jang, S.S.; Hirsh, D.C.: Rapidly growing members of the genus Mycobacterium affecting dogs and cats. JAAHA 38 (3):217-220; 2002.

14. Kirschner, P.; Bottger, E.C.: Species identification of mycobacteria using rDNA sequencing. Methods Mol. Biol. 101:349-361; 1998.

15. Bonenberger, T.E. et al.: Rapid identification of tissue micro-organisms in skin biopsy specimens from domestic animals using polyclonal BCG antibody. Vet. Dermatol. 12 (1):41-47; 2001.


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