What is the likely cause and appropriate work‑up for a 55‑year‑old woman with annual episodes of unilateral facial, lip, and neck swelling that follow a brief headache and resolve spontaneously?

Recurrent Unilateral Facial Swelling: Likely Diagnosis and Work-Up

This patient's presentation is most consistent with either hereditary angioedema (HAE) or a rare lymphatic disorder such as spontaneous cervical swelling syndrome (SCSS), and you should immediately obtain C4, C1 inhibitor antigenic and functional levels to rule out HAE, which carries mortality risk from laryngeal involvement.

Clinical Pattern Analysis

The 20-year history of annual, self-limited episodes with a stereotypical pattern (headache prodrome → unilateral facial/lip/neck swelling → spontaneous resolution over days) is critical. This recurrent, episodic nature with complete resolution between attacks points away from progressive structural lesions or chronic inflammatory conditions.

Key Differential Considerations

Hereditary Angioedema (HAE):

• While the annual frequency is unusually low for typical HAE (most patients have more frequent attacks), the pattern of swelling that worsens over 24 hours, peaks, then resolves over 48 hours matches HAE precisely 1
• HAE attacks can be preceded by a prodrome, which could explain the headache 1
• The involvement of face, lip, and neck is classic for HAE 1
• Critical point: HAE carries mortality risk if laryngeal swelling occurs, making this diagnosis essential to exclude 1

Spontaneous Cervical Swelling Syndrome (SCSS):

• This rare disorder predominantly affects adult women (mean age 56 years) with unprovoked, self-limiting, often unilateral cervical edema 2
• Episodes are acute onset with mean duration of 3.8 days and demonstrate diffuse edema in supraclavicular and infrahyoid regions 2
• No laboratory abnormalities are found 2
• This matches your patient's presentation remarkably well

Melkersson-Rosenthal Syndrome/Cheilitis Granulomatosa:

• Presents with facial/lip swelling but typically becomes more persistent over time rather than completely resolving 3, 4
• Often associated with plicated tongue and facial palsy 3, 4
• Less likely given the complete resolution between episodes

Recommended Diagnostic Work-Up

First-Line Laboratory Testing (Mandatory):

1. C4 level - screening test for HAE; will be low in both type I and type II 1
2. C1 inhibitor antigenic level - low in type I HAE, normal in type II 1
3. C1 inhibitor functional level - low in both type I and type II HAE 1
4. C1q level - should be normal in HAE (helps distinguish from acquired C1 inhibitor deficiency) 1

Critical caveat: These tests should ideally be drawn when the patient is asymptomatic, as acute phase reactants can affect results. If HAE is confirmed, this patient requires immediate access to on-demand HAE-specific treatment given the face/neck involvement and potential for laryngeal compromise 1.

Second-Line Imaging (If HAE excluded):

1. Lymphoscintigraphy during an acute episode - can document impaired lymphatic drainage in SCSS or Melkersson-Rosenthal syndrome 3, 2

   • In SCSS, shows tracer accumulation in supraclavicular region during attacks 2
   • May be normal between episodes 2

2. CT or MRI of neck during acute episode - demonstrates diffuse edema pattern and excludes structural lesions 2

Additional Considerations:

• Complete blood count, comprehensive metabolic panel - to exclude systemic inflammatory conditions
• Tryptase level (during and after episode) - if considering mast cell-mediated angioedema
• Detailed medication history - to exclude ACE inhibitor-associated angioedema (though the 20-year history and annual frequency make this unlikely)

Why This Approach Matters

The distinction between HAE and SCSS is critical for mortality risk. HAE patients can develop life-threatening laryngeal edema and require specific treatment with C1INH concentrates, plasma kallikrein inhibitors, or bradykinin B2 receptor antagonists 1. Standard treatments like epinephrine, corticosteroids, and antihistamines are ineffective in HAE 1.

If HAE is excluded and SCSS is suspected, the condition is benign and self-limited, requiring only reassurance and observation 2. However, you cannot make this assumption without laboratory confirmation.

Start with the C4 level immediately - it's the most cost-effective screening test. If low, proceed with C1 inhibitor testing. If all HAE testing is normal, consider lymphoscintigraphy during the next episode to document SCSS.