Severe rash after COVID-19 vaccination

Diagnosis: Guttate psoriasis

Punch biopsies were obtained, and histopathology revealed diffuse compact hyperkeratosis with broad zones of parakeratosis. There was attenuation of the granular layer and regular elongation of the rete ridges associated with thinning of the suprapapillary epidermis and mild spongiosis. These pathologic findings were consistent with a diagnosis of psoriasis. There were no drug-related skin eruption features, such as apoptotic keratinocytes, eosinophils, or interface dermatitis. Periodic acid-Schiff stains for fungal organisms were negative. The combined clinical presentation (itchy, teardrop-shaped, scaly lesions) and histologic impression were consistent with guttate psoriasis.

Psoriasis can be seen in various forms. Subtypes of psoriasis include guttate psoriasis, inverse psoriasis, erythrodermic psoriasis, nail psoriasis, and pustular psoriasis.¹ Guttate psoriasis accounts for about 2% of psoriasis cases and usually is seen in patients younger than 30 years.² Guttate psoriasis is characterized by 1- to 10-mm teardrop-shaped pink papules with fine scaling.³

One study found that the average time of new onset of psoriasis or flare-up can be between 5 to 14 days after the COVID-19 vaccination.

Triggers for psoriasis. Vaccinations, medications, and infections (eg, group A beta-hemolytic streptococcal upper respiratory infections) can trigger guttate psoriasis.³ MRNA vaccines (eg, Moderna and Pfizer/BioNTech COVID-19 vaccines) have been associated with psoriasis episodes.¹ Other vaccines such as influenza, rubella, bacillus Calmette-Guerin, tetanus-diphtheria, and pneumococcal polysaccharide also have been known to trigger psoriasis.⁴ Medications that can trigger psoriasis include beta-blockers, lithium, antimalarial drugs, and (in some cases)­ nonsteroidal anti-inflammatory drugs.⁵

The impact of COVID-19 vaccine. We are still learning about the incidence and prevalence of adverse effects (such as psoriasis) that can follow COVID-19 vaccination. One study found that the average time of new onset­ of psoriasis or flare-up can be between 5 to 14 days after COVID-19 vaccination.⁶

Psoriasis following vaccination. The pathologic mechanism for the new onset or flare of psoriasis after COVID-19 vaccination is unknown. What is known is that the dysregulation of Th-1 and Th-17 plays an important role in the pathogenesis of psoriasis.⁷ Previously, it was found that psoriasis can manifest after tetanus-diphtheria vaccines due to an increase in the production of Th-17 cells.⁷ Th-1 and Th-17 production also increases after influenza vaccine and can cause an onset or flare-up of psoriasis.⁸

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