What is the diagnosis and management for a 22-year-old male with a 2-day history of itchy, dull painful red spots on his hands and feet, with no known exposure to offending substances, and a past medical history (PMHx) notable for no family history of similar diseases, no bleeding disorders, and no history of chickenpox, presenting with diffuse pinpoint pimple-like lesions and irregular red borders?

Diagnosis: Hand-Foot-Mouth Disease (HFMD) vs. Rocky Mountain Spotted Fever (RMSF)

The most likely diagnosis is Hand-Foot-Mouth Disease (HFMD), but Rocky Mountain Spotted Fever must be immediately excluded given the potentially fatal consequences of delayed treatment. 1

Immediate Life-Threatening Exclusion Required

If fever develops, initiate doxycycline immediately without waiting for confirmation, as RMSF carries 5-10% mortality if untreated. 1, 2

Critical Red Flags for RMSF:

• Fever (typically high-grade) with headache, malaise, or myalgias 1
• Rash that began as blanching pink macules evolving to maculopapules 2-4 days after fever onset 1
• Recent tick exposure or outdoor activities in endemic areas 1
• Progression to petechiae (indicates severe disease) 1

Your patient currently lacks fever and systemic symptoms, making RMSF less likely, but this must be monitored closely. 1

Most Likely Diagnosis: Hand-Foot-Mouth Disease

Supporting Features in Your Patient:

• Distribution confined to hands and feet - highly characteristic of HFMD 3
• Pinpoint pimple-like lesions with white centers - consistent with vesicular evolution from pink macules 3
• Blanching red borders - matches early vesicular stage 3
• 2-day duration with increasing lesions - typical progression 3
• Age 22 years - HFMD predominantly affects children but can occur in adults 3
• No chickenpox history - makes varicella less likely 1

Key Distinguishing Features:

The vesicles in HFMD begin as small pink macules that evolve into vesicular lesions with highly characteristic distribution on palms and soles, subsequently rupturing and causing desquamation. 3

Alternative Diagnoses to Consider

Erythema Multiforme (EM):

• Presents with targetoid lesions from onset (not evolving from macules) 4
• Your patient's lesions have "irregular red borders" which could represent target-like appearance 4
• However, EM typically has more pronounced central clearing and dusky centers 4

Erysipeloid:

• Caused by handling fish, marine animals, or poultry 4
• Typically unilateral on fingers/hands with centrifugal spread 4
• Can develop blue ring with peripheral red halo giving target appearance 4
• Your patient denies occupational exposure and has bilateral involvement, making this unlikely 4

Contact Dermatitis:

• Patient denies contact with offending substances 2
• Would expect more localized distribution based on exposure pattern 1
• Patch testing would be indicated only if recalcitrant or atypical distribution 1

Diagnostic Algorithm

Step 1: Assess for Systemic Symptoms (IMMEDIATELY)

• Temperature measurement - fever mandates empiric doxycycline for presumed RMSF 1, 2
• Headache, malaise, myalgias, nausea, vomiting 1
• Altered mental status, abdominal pain, conjunctival injection 1

Step 2: Detailed Exposure History

• Tick exposure or outdoor activities in past 2 weeks (5-10 day incubation for RMSF) 1
• Travel to endemic areas 1
• Sick contacts with similar symptoms 1
• Occupational exposure to fish/marine animals/poultry 4
• Recent medication use (including chemotherapy) 2

Step 3: Examine Oral Mucosa

• HFMD typically includes oral lesions (though not always present) 4
• Absence of oral lesions does not exclude HFMD 3

Step 4: Monitor Rash Evolution

• HFMD vesicles rupture and cause desquamation over 7-10 days 3
• RMSF progresses to petechiae by day 5-6 if untreated 1
• Document daily progression with photographs 1

Management Plan

If Fever or Systemic Symptoms Present:

Initiate doxycycline 100mg twice daily immediately without waiting for laboratory confirmation. 1, 2 Delay in treatment dramatically increases mortality. 1

If No Fever (Current Scenario):

Supportive Management for Presumed HFMD:

• Fever control with acetaminophen or ibuprofen as needed 3
• Adequate hydration 3
• Reassurance that disease is self-limiting, resolving in 7-10 days 3
• Topical emollients for comfort 2

Close Monitoring Instructions:

• Return immediately if fever develops 1, 2
• Daily self-examination for rash progression to petechiae 1
• Follow-up in 48-72 hours to reassess 1

If Recalcitrant or Atypical Features:

• Consider skin biopsy to exclude neutrophilic dermatosis, vasculitis, or atypical infections 1
• Patch testing if contact dermatitis suspected and history/distribution suggestive 1

Critical Pitfalls to Avoid

Do not assume all palmoplantar rashes are benign - RMSF can be rapidly fatal if missed. 1, 2 The absence of fever at initial presentation does not exclude RMSF, as rash typically appears 2-4 days after fever onset, but some patients present with rash before fever. 1

Do not delay doxycycline if fever and tick exposure are present, even without confirmed diagnosis. 1, 2 Mortality increases dramatically with treatment delay. 1

Do not confuse HFMD with Kawasaki disease - HFMD has discrete vesicles, not diffuse erythema. 3

Do not prescribe antibiotics empirically without clear indication - HFMD is viral and self-limiting. 3 However, if RMSF is suspected, doxycycline is both diagnostic and therapeutic. 1