A 7-year-old boy from Tamil Nadu presents to the emergency department with acute onset severe pain in both hands and feet, swelling, and fever (38.5°C). His mother reports he was well until 6 hours ago. On examination, his hands and feet are warm, swollen, and exquisitely tender. His hemoglobin is 7.2 g/dL, reticulocyte count 8%, and peripheral blood smear shows sickle cells and target cells. X-ray of hands shows no fractures but soft tissue swelling. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Dactylitis (Hand-Foot Syndrome) ### Presentation Recognition **Key Point:** Dactylitis is the acute painful swelling of hands and feet in young children with sickle cell disease, typically occurring between 6 months and 2 years of age, but can occur up to age 8–10 years. This 7-year-old boy presents with the classic triad: 1. Acute onset severe pain in hands and feet 2. Swelling and warmth (infarction-induced inflammation) 3. Fever (from tissue necrosis and inflammatory response) ### Pathophysiology **High-Yield:** Dactylitis results from **vaso-occlusive crisis** in the small bones of hands and feet due to sickling of RBCs in the microvasculature, leading to: - Bone marrow infarction - Acute inflammation - Edema and pain - Often accompanied by systemic signs (fever, elevated WBC) ### Diagnostic Clues | Feature | Finding | Significance | |---------|---------|---------------| | Age | 7 years | Peak incidence 6 months–2 years, but can extend to 8–10 years | | Presentation | Bilateral hands and feet | Symmetrical involvement typical | | Hemoglobin | 7.2 g/dL | Consistent with chronic hemolysis in SCD | | Reticulocyte count | 8% | Elevated (normal <2%), confirms hemolysis | | Smear | Sickle cells, target cells | Diagnostic of sickle cell disease | | X-ray | Soft tissue swelling, no fracture | Rules out trauma; shows infarction pattern | **Clinical Pearl:** Unlike osteomyelitis, dactylitis in SCD is typically **sterile** (infarction-related, not infection-related), though secondary infection can occur. Blood cultures are usually negative unless Salmonella or Staphylococcus is isolated (rare). ### Management Approach ```mermaid flowchart TD A[Child with SCD + acute hand-foot swelling]:::outcome --> B{Fever + elevated WBC?}:::decision B -->|Yes| C[Dactylitis likely]:::outcome C --> D[Supportive care]:::action D --> E[Analgesia, hydration, rest]:::action E --> F[Resolve in 1-2 weeks]:::outcome B -->|No| G[Consider other causes]:::action ``` **Mnemonic:** **DACTYLITIS = Digits + Acute + Crisis + Tender + Young + Lysis + Infarction + Tissue + Inflammation + Swelling** ### Key Distinguishing Features **Warning:** Do NOT confuse dactylitis with: - **Osteomyelitis:** Would show bone destruction on X-ray, positive blood cultures (Salmonella in SCD), focal warmth over bone; dactylitis shows soft tissue swelling only. - **Rheumatoid arthritis:** Symmetric small joint involvement, but occurs in older children/adults, with morning stiffness and positive RF/anti-CCP; dactylitis is acute and systemic. [cite:Robbins 10e Ch 14]