Is a biopsy showing irregular acanthosis, parakeratosis, mild superficial perivascular and lichenoid infiltrate of small lymphocytes, and extravasation of dermal erythrocytes in a patient with a history of psoriasis vulgaris, previously well-controlled on risankizumab (an interleukin-23 inhibitor), considered a partially treated case or a relapse after stopping medication?

Histopathologic Interpretation in Psoriasis After Treatment Discontinuation

This biopsy represents a relapsed case of psoriasis vulgaris following treatment discontinuation, not a "partially treated" case. The histopathologic findings are consistent with active psoriasis that has recurred after stopping risankizumab therapy for 6 months to one year 1.

Understanding the Biopsy Findings

The histopathologic features you describe are characteristic of active psoriasis, though they may show some attenuation compared to untreated disease:

• Irregular acanthosis and parakeratosis are hallmark features of psoriasis vulgaris, representing the keratinocyte hyperproliferation driven by inflammatory cytokines 1
• Mild superficial perivascular and lichenoid lymphocytic infiltrate reflects the T-cell and dendritic cell activation that underlies psoriatic inflammation 1
• Extravasation of dermal erythrocytes corresponds to the increased vascularity characteristic of psoriatic plaques 2

The descriptor "mild" for the inflammatory infiltrate likely reflects the temporal relationship to recent biologic therapy rather than ongoing treatment effect 2.

Clinical Context: Relapse After Biologic Discontinuation

Psoriasis relapse after stopping biologics is expected and well-documented:

• Patients who discontinue cyclosporine typically relapse within approximately 3 months (median 109-113 days) 1
• Your patient stopped risankizumab for 6-12 months before developing widespread plaques, which is entirely consistent with disease relapse rather than partial treatment 3, 4
• The clinical presentation of "scattered scaly plaques all over the body" represents active, untreated disease that has returned after the therapeutic effect of risankizumab wore off 4, 5

Why This Is NOT "Partially Treated" Psoriasis

A "partially treated" case would imply:

• Ongoing therapy with suboptimal response
• Histologic features showing treatment effect (normalized granular layer, reduced inflammatory infiltrate, decreased acanthosis) alongside residual disease 2

Instead, your patient has:

• Complete cessation of therapy for 6-12 months
• Full clinical relapse with widespread new lesions
• Histologic features of active psoriasis 1, 2

The time interval off medication is sufficient for complete loss of drug effect, as risankizumab is dosed every 12 weeks precisely because its therapeutic effect wanes beyond this interval 4, 6.

Management Implications

Restart risankizumab immediately, given the patient's documented excellent response to this IL-23 inhibitor previously 4, 5:

• Risankizumab demonstrated superior efficacy compared to adalimumab (which failed in this patient) in head-to-head trials 4
• The standard dosing is 150 mg subcutaneously at weeks 0,4, and every 12 weeks thereafter 6
• Patients who restart risankizumab after discontinuation typically regain their previous response 4

Critical Pitfall to Avoid

Do not interpret these histologic findings as suggesting treatment failure or need to switch therapies. The patient already demonstrated that risankizumab provides "excellent control" of symptoms 4. The current flare is a predictable consequence of stopping an effective medication, not evidence of secondary treatment failure 1.

The biopsy confirms active psoriasis and rules out alternative diagnoses (such as drug reaction, eczematous dermatitis, or other inflammatory conditions that might have developed during the treatment-free interval) 1, 7.