Monitoring Response to Therapy
Radiographic worsening is commonly observed soon after initiation of effective antifungal therapy for canine blastomycosis, occurring in almost a quarter of dogs (Crews et al. 2008b).
However, this does not portend a worse outcome (Crews et al. 2008b) and—in the absence of other signs of clinical failure—should not alter management. For this reason, follow-up chest radiography is recommended no sooner than 4-6 weeks after therapy initiation in stable patients (Crews et al. 2008b).Quantitative Blastomyces antigen detection by EIA has been evaluated for monitoring of remission in dogs during and after treatment for blastomycosis (Foy et al. 2014). Foy and colleagues prospectively studied 27 dogs with blastomycosis who were monitored clinically, radiographically, and with detection and quantification of Blastomyces antigen in urine and serum following discontinuation of antifungal therapy; among these, 12 dogs were also monitored from time of therapy initiation (Foy et al. 2014). The investigators found that urine antigen levels dropped dramatically within several months of initiation of antifungal therapy. Seven of 27 dogs (26%) relapsed at a median of 4 months following treatment discontinuation. Five of these had detectable antigenuria at the time of clinical relapse, but only one had rising levels of antigenuria preceding clinically detectable relapse. Moreover, persistence of positive urinary antigen at treatment discontinuation did not predict relapse: only two of seven dogs that relapsed had detectable antigenuria at that treatment discontinuation. On the other hand, five of eight of dogs with antigenuria at the end of therapy did not relapse (Foy et al. 2014). In summary, monitoring urine antigen levels during and/or after discontinuation of therapy is unlikely to add significant value to serial clinical and radiographic evaluations for most dogs with blastomycosis.
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