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- Presentation
Case Study of Diagnostic Error, Cognitive Bias, and a Misdiagnosed Scabies Rash in Dermatology
Description
This case presentation aimed to reduce stigma around diagnostic and treatment mistakes and highlight how cognitive bias, logical fallacy, and clinicopathologic correlation affect dermatology practice. A 56-year-old man developed a progressively worsening, intensely pruritic rash over several months that was initially attributed to a terzepatide drug eruption, then reconsidered as prurigo nodularis or a T-cell lymphoproliferative process after poor response to repeated prednisone, topical steroids, dupilumab, and later methotrexate with PUVA. Biopsies showed a dense dermal lymphocytic infiltrate with eosinophils and weak CD30 positivity, and clonality testing suggested a T-cell process, leading to a working diagnosis of lymphomatoid papulosis. However, when the patient worsened further and developed hand and interdigital lesions, a skin scraping revealed scabies mites, eggs, and feces. Review of the prior biopsy found an intracorneal mite, prompting revision of the pathology interpretation to crusted scabies with a reactive lymphoid infiltrate rather than lymphoma. The patient improved after ivermectin, and the presenters emphasized how prolonged immune-modulating treatment likely altered the presentation and contributed to the diagnostic confusion.
View moreConclusions
- The patient’s months-long rash was initially misattributed to a tirzepatide drug eruption and later to lymphomatoid papulosis, illustrating how premature diagnostic closure can occur in practice.
- A dense dermal lymphocytic infiltrate and even clonal T-cell findings did not represent the primary disease, showing that inflammatory or pseudo-lymphomatous pathology can be secondary to another process.
- The true underlying diagnosis was crusted scabies, which was ultimately proven by skin scraping and retrospectively identified on biopsy.
- The severe lymphoid-appearing reaction was likely a reactive/id-like response to scabies, amplified by prolonged treatment with steroids, dupilumab, and methotrexate.
- The case shows that persistent pruritic eruptions that fail standard therapy should prompt repeated reconsideration of the diagnosis and active search for mimickers such as scabies.
- The presentation’s broader conclusion is that cognitive bias and heuristics can lead clinicians down the wrong diagnostic path, and careful clinicopathologic correlation is essential to avoid prolonged misdiagnosis.