Case Number : Case 4084 - 15 September 2022 Posted By: Saleem Taibjee

Neutrophilic dermatosis, could be pyoderma gangrenosum in the setting of hematological malignancy, rheumatoid arthritis or inflammatory bowel disease.

Need to rule out infection.

Need to exclude fungal, some unusual bacterial and atypical mycobacterial infection. 

Infection especially rapidly growing NTM species (Non-Tubeculous Mycobacteria) like M.Chelonae and others. In the last image the white circular spaces on right lower corner contains possible organisms.

Ultimately special stains and tissue culture is required to confirm. 

Was the patient immunocompromised or on Prednisolone?

Of course infection needs to be ruled out. But I d like to add anaplastic large T cell lymphoma as a mimicker of inflammatory conditions to the DD.

Bacterial  ( staphilo? ) infection for me. 

Congratulations to Saman. Spot on... this was a recent case of confirmed Mycobacterium chelonae. The patient was indeed on methotrexate for severe eczema, and thus immunocompromised. He is a keen gardener, so presumably acquired the infection in that environment. The circular spaces which Saman points out are indeed where to look for the organisms. The ZN stain is shown below. There were numerous organisms suggestive of a fast-grower.

The key message here is that atypical mycobacterial infections do not always show much in the way of granulomatous inflammation, and as in this case, can comprise mostly neutrophils/abscess-like picture. So remember to include a ZN stain also. I have seen cases where Wade-Fite is positive, but ZN is negative. However, the Wade-Fite technique is more difficult, and in fact our own lab has now stopped providing Wade-Fite, but not an issue for this particular case.

Great case, Saleem. Thanks a lot.