What could be causing swelling in hands and toes, non-pruritic (not itchy) rash-like bumps on legs and torso, and chills?

Differential Diagnosis: Swollen Hands and Toes with Non-Pruritic Rash and Chills

This presentation requires immediate evaluation for Rocky Mountain spotted fever (RMSF) or other tickborne rickettsial diseases, which can be fatal if untreated, especially if there has been any outdoor exposure or tick contact in the past 2 weeks. 1, 2

Life-Threatening Causes to Rule Out Immediately

Tickborne Rickettsial Diseases (RMSF, Ehrlichiosis)

• RMSF presents with sudden fever, chills, and headache after 5-10 days incubation, with rash appearing 2-4 days after fever onset as small pink macules evolving to maculopapules on ankles, wrists, and forearms, spreading to palms and soles. 1, 2
• Bilateral periorbital edema and edema of the dorsum of hands and feet are recognized features of RMSF, though less commonly observed. 1
• Mortality is 5-10% if untreated but increases substantially with delayed treatment. 2
• Start doxycycline immediately if RMSF is suspected—do not wait for the classic triad of fever, rash, and tick bite, as only a minority present with all three initially. 2
• Ehrlichiosis causes similar symptoms with palmar/sole involvement in 30% of adults and 60% of children, carrying a 3% case-fatality rate. 2

Meningococcemia

• Neisseria meningitidis can present with fever, chills, and rash involving palms and soles, representing a medical emergency requiring immediate antibiotics. 1, 3

Secondary Differential Diagnoses

Psoriatic Arthritis with Erythrodermic Flare

• Erythrodermic psoriasis presents with superficial exfoliation of palms and soles, pitting edema of lower extremities, and swelling of toes (dactylitis). 1, 4
• Dactylitis appears as uniform swelling of digits due to synovitis, tenosynovitis, and soft-tissue edema, occurring in 16-48% of psoriatic arthritis cases. 4
• Systemic symptoms including chills can accompany severe psoriatic flares. 1
• If psoriatic arthritis with dactylitis is confirmed, first-line treatment is a TNF inhibitor (adalimumab, etanercept, or infliximab) to address both skin and joint manifestations simultaneously. 4

Hand-Foot Syndrome (Drug-Induced)

• Only consider if patient is on chemotherapy agents (capecitabine, 5-FU, doxorubicin, sorafenib, sunitinib). 2
• Presents with redness, marked discomfort, swelling, and tingling in palms, developing within days to weeks after therapy initiation. 2
• Does not typically cause chills or systemic symptoms unless complicated by infection. 2

Infective Endocarditis

• Can present with rash on palms and soles along with fever and chills. 1, 3
• Look for cardiac murmur, history of valvular disease, or IV drug use. 1

Streptobacillus moniliformis (Rat-Bite Fever)

• Causes fever, chills, and rash involving palms and soles. 1, 3
• Requires history of rodent exposure or bite. 1

Critical Diagnostic Algorithm

Step 1: Assess for Tick Exposure and Geographic Risk

• Query recent outdoor activities (backyard, hiking, camping) in the past 2 weeks. 1
• Exposure can occur in patient's own backyard or neighborhood, not just wilderness areas. 1
• Ask about similar illnesses in family members, coworkers, or household pets (especially dogs). 1

Step 2: Characterize the Rash Precisely

• If rash involves palms AND soles with fever and chills, treat empirically for RMSF with doxycycline immediately. 1, 2
• Determine if lesions are maculopapular (flat to slightly raised), petechial (non-blanching pinpoint), or vesicular (fluid-filled). 1, 5
• Check if rash blanches with pressure—non-blanching suggests vasculitis or meningococcemia. 6, 5

Step 3: Examine for Specific Features

• Look for bilateral periorbital edema or edema of dorsum of hands/feet (suggests RMSF). 1
• Assess for uniform digit swelling (dactylitis suggests psoriatic arthritis). 1, 4
• Check for silvery scale on trunk or indurated plaques (suggests psoriasis). 1

Step 4: Immediate Treatment Decision

• If any outdoor exposure in past 2 weeks + fever + rash on extremities: Start doxycycline immediately without waiting for confirmatory testing. 1, 2
• If no tick exposure and patient has known psoriasis or inflammatory arthritis: Consider urgent rheumatology referral for systemic therapy. 4
• If patient on chemotherapy: Grade severity and adjust dosing per oncology protocols. 2

Critical Pitfalls to Avoid

• Never wait for laboratory confirmation before treating suspected RMSF—delayed treatment converts a 5% mortality to potentially fatal outcomes. 2
• Do not dismiss the diagnosis because patient doesn't recall a tick bite—many patients with RMSF have no memory of tick exposure. 1
• Do not assume rash on palms/soles is pathognomonic for any single condition—multiple serious diseases share this feature. 1, 3
• Avoid using systemic corticosteroids alone for suspected psoriatic flare, as they can worsen psoriasis during or after taper. 4
• In darker-skinned patients, the rash may be difficult to visualize—palpate for texture changes and examine mucous membranes. 1

Immediate Next Steps

• If tick exposure possible or uncertain: Start doxycycline 100 mg twice daily immediately. 2
• Obtain complete blood count (thrombocytopenia and leukopenia suggest ehrlichiosis or RMSF). 1
• Blood cultures if infective endocarditis suspected. 1
• Consider skin biopsy only if diagnosis remains unclear after initial evaluation and patient is stable. 1, 7
• Urgent infectious disease or dermatology consultation if diagnosis uncertain and patient has fever. 8, 5