Diagnostic Challenges in Rare Infections and Crystal Deposition in Immunocompromised Patients

Conclusions

• Calcium oxalate crystals in skin tissue can be an important diagnostic clue for Aspergillus infection, especially when fungal hyphae with acute-angle branching are present.
• Primary hyperoxaluria can cause vascular oxalate deposition with skin ischemia and gangrene, but in the presented case the oxalate crystals were actually secondary to cutaneous aspergillosis.
• Calcium phosphate, hyaluronic acid, polylactic acid, and urate have distinct histologic appearances that can be differentiated from oxalate on polarized and routine microscopy.
• In an immunocompromised patient with ulcerated skin lesions, Acanthamoeba should be considered because it can present as cutaneous nodules, ulcers, or eschars and may mimic macrophages histologically.
• Acanthamoebiasis is a rare but treatable free-living protozoal infection, and PCR or immunohistochemical testing may be needed for confirmation when tissue morphology is equivocal.
• Buruli ulcer, cryptococcosis, coccidioidomycosis, and leishmaniasis are important mimickers in ulcerative skin disease, but their clinical and histologic hallmarks distinguish them from Acanthamoeba infection.
• Aggressive multidrug therapy can lead to healing of cutaneous Acanthamoeba infection, even in heavily immunocompromised patients.
• The presentation emphasizes that unusual infections should remain on the differential diagnosis for immunocompromised patients with atypical ulcers or eschars.