Diagnosis: Gnathostomiasis (Migratory Subcutaneous Nodules)
The most likely diagnosis is gnathostomiasis, a parasitic infection characterized by recurrent, migratory, painful or pruritic subcutaneous nodules that move to different locations over days to weeks, affecting both the arms and face. 1
Key Diagnostic Features
The migratory pattern of tender subcutaneous nodules distinguishes gnathostomiasis from other causes of subcutaneous swelling 1:
- Migration pattern: Nodules appear as ill-defined swellings that relocate over time, unlike fixed lesions 1
- Distribution: Can affect both upper extremities and face, which differs from erythema nodosum that predominantly affects anterior tibial areas 1, 2
- Incubation period: Approximately 7 days after exposure to contaminated food 1
Critical Differential Diagnoses to Exclude
Erythema Nodosum
- Presents with bilateral, symmetrical, raised tender nodules (1-5 cm) on anterior tibial areas that do not migrate 3, 2
- Associated with systemic symptoms including fever, malaise, and extreme fatigue 2
- Commonly linked to inflammatory bowel disease (4.2-7.5% of IBD patients) 2
Psoriatic Arthritis with Dactylitis
- Presents with "sausage digit" swelling involving entire digits, not discrete migratory nodules 4
- Associated with psoriatic plaques, nail pitting, and morning stiffness >30 minutes 4
- Multiple tender and swollen joints would be present 4
Tendinopathy
- Presents with well-localized tenderness at tendon insertion sites, not migratory nodules 5
- Pain is load-related and reproducible with specific physical maneuvers 5
Diagnostic Workup
Clinical diagnosis is usually sufficient based on the characteristic migratory pattern, but confirmation can be obtained through 1:
- Travel history: Essential to identify exposure in endemic areas (Southeast Asia, particularly Thailand) 1
- Dietary history: Consumption of raw or undercooked freshwater fish, poultry, or frogs 1
- Complete blood count: May show eosinophilia 1
- Serology: Can be sent to specialized laboratories (e.g., Swiss Tropical and Public Health Institute) if confirmation needed 1
Treatment Protocol
First-line treatment: Ivermectin 200 μg/kg orally daily for 2 days 1
Alternative regimen: Albendazole 400 mg orally twice daily for 21 days 1
- Consider if ivermectin unavailable or contraindicated 1
- Treatment may need repetition if symptoms recur 1
Critical Monitoring and Follow-up
Watch for neurologic complications including 1:
- Meningitis
- Encephalitis
- Myelitis
Schedule follow-up visits to assess for relapse, as gnathostomiasis commonly recurs after initial treatment 1
Common Pitfalls to Avoid
- Do not assume fixed nodules: The hallmark is migration; if nodules remain stationary, reconsider the diagnosis 1
- Do not overlook travel history: Even remote travel to endemic areas is relevant 1
- Do not treat empirically for cellulitis: The migratory pattern excludes typical bacterial infection 1
- Do not delay treatment: Early intervention prevents potential neurologic complications 1