Does eosinophil count typically rise in patients with psoriasis?

Eosinophil Count in Psoriasis

Eosinophil counts do not typically rise in untreated psoriasis, but biologic therapies used to treat psoriasis consistently cause significant increases in peripheral blood eosinophils starting as early as 3 months after treatment initiation.

Baseline Eosinophil Levels in Untreated Psoriasis

The available evidence does not support elevated eosinophil counts as a characteristic feature of untreated psoriasis itself. The provided guidelines focus extensively on eosinophilic esophagitis and other eosinophilic conditions 1, 2, but do not identify psoriasis as a condition associated with baseline eosinophilia.

Treatment-Induced Eosinophilia

Biologic Therapy Effects

The most clinically significant finding is that biologic therapies (TNF-alpha inhibitors and IL-12/23 inhibitors) cause substantial increases in peripheral blood eosinophils:

• Mean eosinophil percentage increases from 1.49% at baseline to 2.29% by 3 months of biologic therapy (p<.001), with this elevation persisting throughout 3 years of treatment 3
• Absolute eosinophil counts rise from 115.80 × 10³/µL to 174.9 × 10³/µL by 3 months (p<.001) and remain elevated at 162.9 × 10³/µL at 36 months 3
• This effect occurs with etanercept, infliximab, adalimumab, and ustekinumab 3
• Biosimilar adalimumab can cause marked eosinophilia, with one case report documenting an increase from 3.2% to 19.9% eosinophils 4

Cyclosporine A Effects (Opposite Direction)

In contrast to biologics, cyclosporine A treatment causes a decrease in eosinophil counts:

• Eosinophils drop from 190/µL to 137/µL after 1 week (p=0.038) and to 127/µL after 10 weeks (p=0.006) of cyclosporine A therapy 5
• This reduction occurs rapidly and may be linked to cyclosporine's antipsoriatic mechanism 5, 6

Clinical Implications and Monitoring

When to Investigate Eosinophilia in Psoriasis Patients

If a psoriasis patient on biologic therapy develops eosinophilia, consider the following algorithm:

• Mild eosinophilia (500-1,500 cells/µL): Likely treatment-related if asymptomatic; no intervention needed but continue monitoring 2
• Moderate eosinophilia (>1,500 cells/µL) or symptomatic: Exclude alternative causes including:
  • Parasitic infections (stool microscopy, serology based on travel history) 2
  • Drug hypersensitivity reactions beyond expected biologic effect 4
  • Concurrent atopic conditions (allergic rhinitis, asthma, eczema) that may independently elevate eosinophils 1
  • Eosinophilic esophagitis if gastrointestinal symptoms present (requires endoscopy with biopsies showing >15 eosinophils per 0.3 mm²) 2

Management Approach

• Asymptomatic eosinophilia during biologic therapy: Continue treatment with periodic monitoring, as this appears to be an expected pharmacologic effect without clinical significance 3
• Symptomatic or marked eosinophilia: Discontinue the biologic agent and observe for normalization of counts, as demonstrated in the adalimumab case where eosinophils normalized after drug cessation 4
• Persistent eosinophilia after excluding secondary causes: Consider hematology referral if eosinophilia persists >3 months after stopping the offending agent 7

Important Caveats

• Peripheral blood eosinophil counts may not correlate with tissue eosinophilia in conditions like eosinophilic esophagitis, so tissue biopsy remains necessary if this diagnosis is suspected 1, 2
• The increase in eosinophils with biologic therapy does not correlate with treatment efficacy or disease severity 3
• Eosinophil activation markers (like ECP) may remain elevated or increase despite antipsoriatic treatment, even when absolute counts change 5