MPO-ANCA Positivity in a Patient with Pyoderma Gangrenosum and Graves’ Disease: A Case Report and Review of the Literature

Background Pyoderma gangrenosum is an ulcerative cutaneous condition most commonly associated with inflammatory bowel disease, but it can also be associated with rheumatologic disease and other systemic illnesses.[1] Rarely has it been reported in ANCA-associated vasculitides (AAV), usually with an anti-PR3 antibody pattern.[2] Given the infrequency of this association, a thorough search should be undertaken for other underlying causes before pyoderma gangrenosum is attributed to AAV in patients with positive ANCAs. Case A 73-year-old woman with a history of Graves’ disease treated 5 years prior with propylthiouracil and methimazole presented with ulcerative lesions of the flank and perineal area. Rheumatology assessment was triggered on account of her having a positive anti-MPO ANCA antibody. Further workup including testing for antiphospholipid antibodies, hepatitis B and C, HIV, and syphilis, were all negative. On review she had no clinical evidence of inflammatory bowel disease or another systemic rheumatologic condition, specifically, no evidence of ANCA vasculitis. Biopsy of the skin lesions was compatible with pyoderma gangrenosum. She was started on prednisone 50 mg daily for 2 weeks followed by a taper. At the most recent assessment 6 months later she had completed the prednisone and was using Protopic only, with almost complete healing of her skin lesions. Thyroid biochemistry revealed hyperthyroidism, suggesting recurrence of Graves’ disease as a possible trigger for the pyoderma gangrenosum. Although the association between antithyroid medications and development of AAV is widely known, the lengthy interval since this patient received these treatments made their implication less likely. Conclusion The discovery of autoantibodies such as ANCAs in a patient with otherwise non-specific clinical manifestations of disease is a common cause for rheumatology consultation. Although pyoderma gangrenosum can be a manifestation of AAV, the pattern of anti-MPO rather than anti-PR3 positivity made this less likely in this case. Given that further workup revealed no other features of systemic AAV, investigation for non-rheumatologic causes of pyoderma gangrenosum was undertaken, which revealed recurrence of the patient’s previously treated Graves’ disease. Pyoderma gangrenosum is known to occur in a small number of Graves’ disease patients and can occur as its initial manifestation.[1] Furthermore, ANCA positivity is common in Graves’ disease, especially of the anti-MPO pattern, which further supports the conclusion that the ANCA positivity seen in this patient was incidental to thyroid disease, and not suggestive of AAV.[3] This case demonstrates the importance of an awareness of non-rheumatologic causes for both pyoderma gangrenosum and ANCA positivity. [1.] Livideanu C. Clin Dermatol 2006;31:659-61. [2.] Shakshouk H. Clin Exp Dermatol 2022;47:1716-9. [3.] Gumà M. J Clin Endocrinol Metab 2003;88:2141-6.

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