In the Chair: Hereditary Angioedema and CSU

Hereditary angioedema and chronic spontaneous urticaria are well-established diagnoses and, by clinical dogma, mutually exclusive ones. Classic teaching holds that HAE does not present with urticaria, and that angioedema in a confirmed CSU patient is simply a manifestation of that disease.¹ When both conditions coexist, the assumption is that one explains the other.

But what happens when the angioedema doesn’t behave like the urticaria? This case, published in Clinical Case Reports, follows a 26-year-old woman whose refractory skin disease had more than one diagnosis — and whose second one was nearly missed because the first one was already confirmed.²

Work through the clinical decision points below. At each step, consider what you’d do — then see how the case unfolded and why.

The Patient

A 26-year-old woman presents with a 1-year history of recurrent erythema and pruritus of the trunk and limbs. Wheals appear without obvious triggers, are worsened by scratching, and resolve spontaneously. There is no significant family history and no known allergic history. She has not responded to first-line antihistamines.

CLINICAL DECISION POINT 1—Refractory Urticaria

Your patient has had recurrent wheals and pruritus for more than a year. Antihistamines have failed. She has no identifiable trigger and no relevant personal or family history.

📋WHAT WOULD YOU DO?

CLINICAL DECISION POINT 2—A Different Kind of Swelling

Your patient’s urticaria is now well controlled, however, during her follow-up visits, she mentions something she considers separate: recurrent, mild swelling of the lips and face. The episodes have no identifiable trigger — though she notices they sometimes occur after yawning. The swelling is not accompanied by wheals or pruritus. It resolves on its own in approximately 30–40 minutes. Importantly, these episodes do not correlate with her urticaria flares.

📋WHAT WOULD YOU DO?

CLINICAL DECISION POINT 3—Interpreting the Lab Results

You order a targeted workup. Thyroglobulin and ANA are negative. Results return as follows:

• C4: 25 mg/L (reference: 100–400 mg/L)
• C1-INH: 0.08 g/L (reference: 0.21–0.39 g/L)

Both values are significantly below the lower limit of normal.

📋WHAT WOULD YOU DO?

CLINICAL DECISION POINT 4—Confirmed Dual Diagnosis — Now What?

Your patient now has confirmed diagnoses of both CSU and HAE-C1-INH. Her CSU is well controlled on omalizumab. Her HAE-related angioedema episodes are mild, self-resolving within 30–40 minutes, and she reports that her quality of life is not significantly affected by them. She is not currently on any HAE-specific therapy.

📋WHAT WOULD YOU DO?

Clinical Takeaway: When to Suspect HAE in a Patient with Urticaria or Angiodema

✓Angioedema that occurs independently of urticaria activity — especially without wheals or pruritus

✓Episodic swelling that resolves in under 1 hour and does not respond to antihistamines, glucocorticoids, or omalizumab

✓Swelling triggered by physical pressure, stress, or minor trauma (yawning, dental procedures)

✓Low complement C4 on routine labs — even incidentally detected

✓No family history does not exclude HAE; sporadic SERPING1 mutations are a recognized etiology

✓Confirmed CSU does not rule out concurrent HAE — the two conditions can coexist

The Bottom Line

This case challenges one of the more durable assumptions in dermatologic practice: that HAE and CSU don’t coexist. The clinical dogma that urticaria in a patient with angioedema points away from HAE has real diagnostic consequences — in a Danish retrospective cohort, half of HAE patients with erythema marginatum had their rash misdiagnosed as urticaria, and a quarter experienced urticaria-like prodromal symptoms.⁵ When the first diagnosis explains most of the picture, it’s easy to stop looking.

What allowed the correct diagnosis here was paying attention to what didn’t fit. The angioedema episodes were behaviorally distinct from the urticaria: no wheals, no pruritus, no correlation with CSU flares, and a resolution timeline more consistent with bradykinin-mediated swelling than histamine. That dissociation was the diagnostic signal. A targeted lab workup — C4, C1-INH, and genetic testing — confirmed what the clinical picture was already suggesting.

For clinicians managing patients with refractory or complex skin disease, this case is a reminder that a confirmed diagnosis should not function as a diagnostic ceiling. When something doesn’t fit the known picture, it may be pointing to something else entirely.

References

1. Bernstein JA, Ansotegui I, Asero R, et al. Diagnostic testing for chronic spontaneous urticaria with or without angioedema: The do's, don't and maybe's. World Allergy Organ J. 2025;18(7):101068. Published 2025 Jun 9. doi:10.1016/j.waojou.2025.101068
2. Wang H, Shen Y. Case report: Hereditary angioedema accompanied by chronic spontaneous urticaria. Clin Cosmet Investig Dermatol. 2026;19:581977. Published 2026 Mar 23. doi:10.2147/CCID.S581977
3. Labrador-Horrillo M, Ferrer M. Profile of omalizumab in the treatment of chronic spontaneous urticaria. Drug Des Devel Ther. 2015;9:4909-4915. Published 2015 Aug 25. doi:10.2147/DDDT.S56004
4. Bhivgade S, Melkote S, Ghate S, Jerajani HR. Hereditary angioedema: not an allergy. Indian J Dermatol. 2012;57(6):503. doi:10.4103/0019-5154.103081
5. Rasmussen ER, de Freitas PV, Bygum A. Urticaria and prodromal symptoms including erythema marginatum in Danish patients with hereditary angioedema. Acta Derm Venereol. 2016;96(3):373-376. doi:10.2340/00015555-2233