What is the diagnosis and management for a patient with rhinovirus positivity and a rash on the soles of the feet and body?

Rhinovirus with Rash on Soles and Body: Diagnosis and Management

Primary Diagnosis

This presentation is most consistent with hand-foot-and-mouth disease (HFMD) caused by enteroviruses or coxsackieviruses, which can co-occur with rhinovirus detection. 1, 2

The combination of rhinovirus positivity with a rash involving the soles of the feet and body strongly suggests HFMD, as rhinovirus itself does not typically cause rash. 1, 3 The rhinovirus detection likely represents either a co-infection or an incidental finding, as rhinovirus is extremely common and causes primarily respiratory symptoms without exanthem. 3, 4

Critical Differential Diagnoses to Exclude Immediately

Before settling on HFMD, you must urgently exclude life-threatening causes of rash involving the soles:

Rocky Mountain Spotted Fever (RMSF)

• Rash on palms and soles indicates advanced RMSF and is associated with severe illness requiring immediate doxycycline. 5, 6
• The classic petechial rash appears by day 5-6 of illness, beginning as small blanching pink macules on ankles, wrists, or forearms that evolve to maculopapular lesions with central petechiae. 6, 7
• Critical pitfall: Up to 20% of RMSF cases lack rash entirely, and only 60% report tick exposure, so absence of these features does not exclude diagnosis. 6, 7
• Look for: fever, severe headache, myalgias, thrombocytopenia, hyponatremia, and elevated hepatic transaminases. 5, 7

Meningococcemia

• Petechial or purpuric rash that rapidly progresses to purpura fulminans alongside high fever, severe headache, and altered mental status. 6, 7
• This progresses more rapidly than RMSF and requires immediate ceftriaxone. 7

Other Serious Causes

• Secondary syphilis (Treponema pallidum), bacterial endocarditis, ehrlichiosis, and rat-bite fever can all cause rash on palms and soles. 5, 6

Diagnostic Algorithm

Step 1: Assess for Systemic Toxicity

• If fever >102°F, severe headache, altered mental status, hypotension, tachycardia, or rapidly progressive rash → start empiric doxycycline immediately and add ceftriaxone if meningococcemia cannot be excluded. 7
• Do not wait for laboratory confirmation or the classic triad of fever, rash, and tick bite. 6, 7

Step 2: Characterize the Rash

• HFMD: Maculopapular or papulovesicular rash on hands and soles, painful oral ulcerations, low-grade fever. 1, 2
• RMSF: Begins on ankles/wrists/forearms, evolves to petechiae by day 5-6, involves palms and soles late in disease. 5, 6
• Meningococcemia: Petechial/purpuric rash with rapid progression. 6, 7

Step 3: Obtain Targeted History

• Tick exposure (though only 60% of RMSF cases report this). 7
• Recent outdoor activities in grassy/wooded areas. 5
• Contact with other children with similar rash (suggests HFMD). 1, 8
• Time of year: HFMD peaks spring to fall; RMSF peaks April-September. 5, 1
• Timing of rash relative to fever: HFMD rash appears with or shortly after fever; RMSF rash appears 2-4 days after fever onset. 5, 1

Step 4: Laboratory Studies

• If RMSF or meningococcemia suspected: CBC with differential (look for thrombocytopenia, bandemia), comprehensive metabolic panel (hyponatremia, elevated transaminases), blood cultures. 5, 7
• Acute serology for R. rickettsii, E. chaffeensis, A. phagocytophilum (but do not wait for results to treat). 5
• If HFMD suspected: No specific testing required; diagnosis is clinical. 1

Management

If HFMD is Confirmed (No Systemic Toxicity)

• Treatment is supportive: hydration and pain relief with acetaminophen or ibuprofen. 1
• Oral lidocaine is not recommended. 1
• Lesions typically resolve in 7-10 days. 1
• Counsel families about potential nail dystrophies (Beau's lines, nail shedding) weeks after symptom onset. 2, 8
• Prevent spread through handwashing and disinfecting surfaces. 1

If RMSF Cannot Be Excluded

• Start doxycycline immediately (even in children <8 years old) without waiting for laboratory confirmation. 7
• Hospitalize if systemic toxicity, rapidly progressive rash, or diagnostic uncertainty. 7
• 50% of RMSF deaths occur within 9 days of illness onset; delay in treatment significantly increases mortality. 7

If Meningococcemia Cannot Be Excluded

• Start ceftriaxone immediately. 7
• Hospitalize for close monitoring. 7

Common Pitfalls to Avoid

• Do not dismiss rash on soles as benign without excluding RMSF and meningococcemia first. 5, 6
• Do not wait for the classic triad of fever, rash, and tick bite in RMSF—it is present in only a minority of patients at initial presentation. 6, 7
• Rash on palms and soles is not pathognomonic for any single condition—consider multiple serious causes. 5, 6
• In darker-skinned patients, petechial rashes may be difficult to recognize, increasing risk of delayed diagnosis. 6
• Rhinovirus detection does not explain the rash—look for the true cause. 3, 4
• Absence of tick exposure does not exclude RMSF. 7