What is the diagnosis and treatment for painful migrating tender nodules in the upper and lower limbs?

Diagnosis: Gnathostomiasis

The most likely diagnosis for painful migrating tender nodules in the upper and lower limbs is gnathostomiasis, a parasitic infection caused by Gnathostoma species, which characteristically presents with recurrent pruritic or painful, ill-defined migratory subcutaneous nodules. 1

Clinical Presentation

• Recurrent painful or pruritic subcutaneous nodules that migrate over time, typically appearing as ill-defined swellings under the skin 1
• Migration pattern distinguishes this from other causes of subcutaneous nodules—the nodules move to different locations over days to weeks 1
• Distribution can affect both upper and lower extremities, unlike erythema nodosum which predominantly affects the anterior tibial areas 1, 2
• Incubation period of approximately 7 days after exposure 1

Key Differential Diagnoses to Exclude

Erythema Nodosum

• Presents with tender, raised, red or violet nodules of 1-5 cm diameter that are typically bilateral and symmetrical on the anterior tibial areas 1, 2
• Does NOT migrate—this is the critical distinguishing feature 2, 3
• Usually associated with systemic symptoms including fever, malaise, and arthralgia 2, 4
• Commonly linked to streptococcal infections, sarcoidosis, inflammatory bowel disease, or medications 3, 5

Trichinellosis

• Presents with facial and periorbital edema, urticarial rash, severe myalgia, and muscle weakness in the parenteral phase 1
• Preceded by gastrointestinal symptoms (diarrhea) in the enteral phase 1
• Less likely if nodules are the predominant feature without significant myositis 1

Diagnostic Approach

• Clinical diagnosis is usually sufficient based on the characteristic migratory pattern of subcutaneous nodules 1
• Serology is not available in the UK but can be sent to the Swiss Tropical and Public Health Institute if confirmation is needed 1
• Travel history is essential—gnathostomiasis is endemic in Southeast Asia, particularly Thailand, and transmission occurs through consumption of raw or undercooked freshwater fish, poultry, or frogs 1
• Eosinophilia may be present on complete blood count 1

Treatment

Seek expert advice and treat with ivermectin 200 μg/kg PO daily for 2 days with monitoring for relapse. 1

Alternative Regimen

• Albendazole 400 mg PO twice daily for 21 days can be used as an alternative 1
• Treatment may need to be repeated if symptoms recur, as the parasite can be difficult to eradicate completely 1

Monitoring

• Follow-up is essential to assess for relapse, as gnathostomiasis can recur after initial treatment 1
• Watch for neurologic complications including meningitis, encephalitis, or myelitis, which occur rarely but require urgent management 1

Common Pitfalls to Avoid

• Do not mistake this for erythema nodosum—the migration pattern is pathognomonic for gnathostomiasis, whereas erythema nodosum lesions remain fixed 1, 2
• Do not delay treatment while waiting for serologic confirmation, as clinical diagnosis is reliable and serology may not be readily available 1
• Do not assume a single course of treatment is sufficient—monitor for relapse and be prepared to retreat 1
• Do not overlook travel history—failure to elicit exposure to endemic areas may lead to misdiagnosis 1