A single patient case, published this month in Cureus, has reopened a clinical question dermatologists rarely face: what happens when a biologic clears one disease and ignites another? The report describes atopic dermatitis emerging in an adult receiving ustekinumab for ulcerative colitis, then reviews the targeted therapies now available when inflammatory bowel disease and chronic skin disease collide in the same body.

Ustekinumab is a human monoclonal antibody directed against the p40 subunit shared by interleukin-12 and interleukin-23. It carries FDA approvals for moderate-to-severe plaque psoriasis, psoriatic arthritis, Crohn disease, and ulcerative colitis. Its dual blockade of the IL-12/Th1 and IL-23/Th17 axes has made it a workhorse for patients with overlapping immune-mediated disease.

What does the report actually describe?

The Cureus article is a case report plus narrative review. The authors document a patient with ulcerative colitis who developed atopic dermatitis while on ustekinumab maintenance therapy. They then walk through the targeted agents that clinicians can consider when atopic dermatitis and inflammatory bowel disease coexist in one patient.

The authors did not release patient-level severity scores, treatment duration, or the specific time to dermatitis onset in the publicly available title and metadata. Those granular data points live inside the full PDF. For practicing dermatologists, the value sits less in the single patient than in the decision tree the review lays out.

Why is this clinically awkward?

Ustekinumab typically helps eczema-adjacent disease. The drug's IL-23 inhibition has shown signal in atopic dermatitis trials, and a parallel IL-23 pathway is implicated in barrier-driven inflammation. A paradoxical flare of atopic dermatitis on the drug therefore reads as counterintuitive.

Paradoxical reactions are well documented in dermatology. Patients on TNF inhibitors can develop new psoriasis. Patients on IL-17 blockers can develop eczematous eruptions. Each class has a fingerprint of unintended skin effects. Case reports are how that fingerprint gets mapped, one patient at a time.

How do the targeted therapies stack up across both diseases?

The review's central service is a side-by-side look at biologics and small molecules with activity in both ulcerative colitis and atopic dermatitis. No single agent yet carries dual FDA labeling, so prescribers must choose a primary indication and accept off-label benefit on the other.

• Dupilumab is approved for moderate-to-severe atopic dermatitis and has growing data in ulcerative colitis, where phase 3 trials reported clinical remission in a defined share of patients and FDA review for the IBD indication is in motion.
• Tralokinumab and lebrikizumab, the newer IL-13 antibodies, are approved for atopic dermatitis. Their IBD profiles remain under study, with no approved indication.
• JAK inhibitors such as upadacitinib and tofacitinib carry approvals on both sides of the aisle. Upadacitinib is approved for atopic dermatitis and for ulcerative colitis; tofacitinib carries the ulcerative colitis label and has atopic dermatitis data, though the FDA declined to expand the dermatology indication.
• Risankizumab and mirikizumab, the selective IL-23 blockers, are approved for ulcerative colitis and for psoriasis. Their atopic dermatitis data are early and unconvincing.
• Ustekinumab itself remains approved for ulcerative colitis and psoriasis, with no atopic dermatitis label.

The therapeutic landscape offers options, but no clean answer for the patient who needs both conditions controlled at once.

What should a dermatologist do when the report echoes in clinic?

The practical takeaway is short. When a patient on ustekinumab for IBD develops new atopic dermatitis, switching class is one path. Adding a topical regimen is another. The Cureus review frames the decision as a choice between chasing the skin with a second biologic and accepting the off-label benefits of a single agent that straddles both diseases.

Dermatology Times readers who manage complex inflammatory disease will recognize the pattern. Biologic selection has stopped being a single-organ decision. The patient in front of you is one body, and the prescription now lives in the overlap of two specialty guidelines.

What comes next for coexisting-disease management?

The case report and its accompanying review signal a slow shift in how the field treats patients with two immune-driven diagnoses. Registry data and head-to-head biologic trials in overlapping populations remain thin. Until those mature, case reports like this one will keep doing the heavy lifting, one patient at a time.