Table 1.

BP, CSU, PN, and CPUO: diagnosis outline

Diagnosis	Clinical criteria	Clinic visit	Laboratory assessments
BP	• Tense blisters, erosions • Pruritic urticarial plaques • Variable non-bullous pictures, e.g., urticarial or eczematous lesions accompanied by pruritus	Medical history • Patient-reported symptoms and caregiver/family’s supportive narrative • Comprehensive medication history (to assess for potential drug triggers) • Comorbidities and overall functional status • Physical examination	• Perilesional skin biopsy for direct immunofluorescence • Lesional skin biopsy for histopathology (H&E stain) • Serum sample   o Indirect immunofluorescence on salt-split skin   o BP180 ELISA   o BP230 ELISA (when BP180 ELISA negative)
CSU	• Spontaneous appearance of daily or almost daily itchy hives with or without angioedema lasting >6 weeks • Each hive resolves within 24–36 hours with no residual lesion • Absence of fever, malaise, and joint/bone pain	• Provisional CSU diagnosis can be reached via an accurate history of hives occurrence, duration, characteristics, trigger factors, and other ± symptoms • Physical examination includes review of patient photo documentation (pictures of wheals and angioedema)	• Blood tests (CBC, differential blood count, CRP, antithyroid antibodies [antithyroid peroxidase antibodies], total IgE) • In some situations, it is important to exclude inducible urticaria by conducting a specific provocation test. Typically, hives appear only when the trigger contacts the skin and last <2 hours, except in cases of delayed pressure urticaria
PN	• Pruritus lasting ≥6 weeks • Firm, pruritic nodules • History and/or signs of repeated scratching, picking, or rubbing	• Thorough history and examination including review of medications and prior laboratory work • Assess severity: extent of lesions, pruritus intensity, disease burden • If necessary, assess the need for behavioral and emotional support for anxiety or depression	• May include CBC, liver, and renal function tests • Depending on risk factors, review of systems: thyroid function, diabetes assessment, HIV, and hepatitis B and C testing • Additional tests: work-up can be broad based on each patient’s unique medical history
CPUO	• Generalized/non-localized pruritus lasting ≥6 weeks with no identifiable primary rash and often no secondary skin lesions either • Exclusion of primary dermatologic or other underlying medical disorders (e.g., immunologic, systemic, neuropathic, infections, iatrogenic)	Medical history and physical examination • Timing, location, and duration of pruritus; medications and comorbidities (e.g., narcotic use); environmental factors	• CBC with differential and liver, renal, and thyroid function tests • Additional tests: biopsy recommended for any patient with a history of a skin lesion in a pruritic site or if suspicion for latent pruritic dermatosis is high because of history or risk factors   o If malignancy is suspected, refer for malignancy screening   o Refer for neurologic work-up if neurologic cause is suspected

BP bullous pemphigoid, CBC complete blood count, CPUO chronic prurigo of unknown origin, CRP C-reactive protein, CSU chronic spontaneous urticaria, ELISA enzyme-linked immunosorbent assay, H&E hematoxylin and eosin, HIV human immunodeficiency virus, IgE immunoglobulin E, PN prurigo nodularis