Differential Diagnosis for Rash on Hands and Feet

Immediate Life-Threatening Considerations

The Centers for Disease Control and Prevention recommends initiating doxycycline 100 mg twice daily immediately without waiting for laboratory confirmation if fever is present with rash on hands/feet 1, 2
Rocky Mountain Spotted Fever presents with small blanching pink macules on ankles and wrists, progressing to maculopapular with central petechiae that spreads to palms and soles, and carries a 5-10% case-fatality rate 1, 2
Human Monocytic Ehrlichiosis causes rash in only 30% of adults, appearing later and rarely involving palms/soles, and carries a 3% case-fatality rate 1, 2
Critical red flags requiring immediate doxycycline include fever + rash + headache + tick exposure or thrombocytopenia/hyponatremia 2

The British Association of Dermatologists suggests that hand involvement in contact dermatitis results from chronic cumulative irritant exposure to detergents, organic solvents, soaps, or "dry" irritants like powders 3
Occupational dermatitis accounts for 70% of occupational skin disease with hand involvement predominating 3
Palmoplantar psoriasis presents with erythematous inflammatory plaques with silvery scale, and differential from chronic allergic contact dermatitis is difficult, especially with isolated palmoplantar involvement 4, 5

The American Academy of Dermatology notes that enteroviral infections are the most common cause of maculopapular rashes, typically sparing palms, soles, face, and scalp 2, 6
Human herpesvirus 6 (roseola) presents with macular rash following high fever, and parvovirus B19 causes "slapped cheek" appearance with possible truncal involvement 2, 6

The Centers for Disease Control and Prevention recommends obtaining complete blood count, comprehensive metabolic panel, and acute serology for R. rickettsii, E. chaffeensis, A. phagocytophilum if fever + rash on hands/feet is present 1, 2, 6
Expect clinical improvement within 24-48 hours after starting doxycycline 6

The Centers for Disease Control and Prevention advises against excluding RMSF based on absence of tick bite history, as 40% of patients do not report tick exposure 2
Do not wait for serologic confirmation before starting doxycycline if RMSF is suspected, as IgM/IgG are not detectable before the second week 7
Do not assume palmoplantar rash is benign, as multiple life-threatening infections present this way 1
Do not rely solely on clinical features to distinguish allergic from irritant contact dermatitis, as patch testing is essential 3