What is the appropriate evaluation and treatment for a patient presenting with facial erythema (red face) and relative monocytosis (elevated relative monocytes)?

Evaluation and Management of Facial Erythema with Relative Monocytosis

This presentation warrants immediate evaluation for tickborne rickettsial diseases, particularly Rocky Mountain Spotted Fever (RMSF) or ehrlichiosis, especially if the patient has outdoor exposure history, and empiric doxycycline should be strongly considered while awaiting confirmatory testing. 1

Initial Differential Diagnosis

The combination of facial erythema and relative monocytosis (9.6%) with normal absolute monocytes creates a specific diagnostic pattern that requires systematic evaluation:

High-Priority Infectious Etiologies

• Tickborne rickettsial diseases (RMSF, ehrlichiosis, anaplasmosis) should be at the top of the differential, as these conditions present with diffuse erythema, fever, and hematologic abnormalities including relative monocytosis. 1
• The presence of diffuse erythema with scabs on the lower extremities, as described in documented RMSF cases, is particularly concerning for tickborne illness. 1
• Even without recalled tick bite (which occurs in the majority of cases), outdoor exposure in wooded areas during summer months significantly increases suspicion. 1

Other Infectious Considerations

• Mycoplasma pneumoniae infection can present with facial erythema and should be ruled out immediately if there are any respiratory symptoms, as it requires specific antibiotic therapy. 2
• Herpes simplex virus (HSV) can trigger erythema multiforme, though this typically presents with target lesions rather than diffuse facial erythema. 2, 3

Non-Infectious Etiologies

• Rosacea commonly presents with facial erythema, particularly affecting malar and nasal areas, but would not explain the monocytosis. 4, 5
• Drug reactions including erythema multiforme or early Stevens-Johnson syndrome must be considered, especially with any recent medication changes. 2, 3

Critical Workup

Immediate Laboratory Assessment

• Complete blood count with differential - already obtained, showing relative monocytosis (9.6%) with normal absolute monocytes, which creates a pattern where other cell lines may be relatively decreased. 1
• Comprehensive metabolic panel including liver function tests (AST, ALT, alkaline phosphatase, bilirubin) and renal function (creatinine) - elevated transaminases and thrombocytopenia are highly suggestive of tickborne rickettsial disease. 1
• Platelet count - thrombocytopenia is a key finding in RMSF and ehrlichiosis. 1
• Blood cultures if febrile to rule out sepsis. 1

Serologic and Molecular Testing

• Acute and convalescent serologic testing for RMSF and ehrlichiosis (IgM and IgG antibodies), recognizing that acute-phase serology may be negative in the first 2 weeks. 1
• PCR testing for tickborne diseases if available, as this can provide earlier diagnosis. 1
• Peripheral blood smear examination looking specifically for intracellular morulae (characteristic of ehrlichiosis) or schistocytes. 1

Physical Examination Details

• Complete skin examination documenting distribution of erythema, presence of any target lesions, vesicles, pustules, or scaling. 1, 6
• Examine all mucous membranes (oral, conjunctival, genital) for involvement, as mucosal lesions would suggest Stevens-Johnson syndrome or other severe cutaneous adverse reactions. 1
• Look for scabs or eschars particularly on lower extremities, which may indicate tick bite sites. 1
• Assess for lymphadenopathy, hepatosplenomegaly which may be present in tickborne diseases. 1

Additional Considerations Based on Monocytosis

• Bone marrow biopsy should be considered if there are unexplained cytopenias or persistent monocytosis, as this can indicate concomitant myeloid neoplasms. 1
• Rule out Erdheim-Chester disease if there are bone lesions, perinephric stranding, or periaortic infiltrates on imaging, though this is rare. 1

Treatment Algorithm

If Tickborne Disease is Suspected (Most Urgent)

Empiric doxycycline should be initiated immediately without waiting for confirmatory testing if there is clinical suspicion based on:

• Outdoor exposure history
• Summer presentation
• Diffuse erythema with or without scabs
• Thrombocytopenia or elevated liver enzymes
• Relative monocytosis with systemic symptoms 1

Dosing: Oral doxycycline for outpatient management, with close follow-up within 24-48 hours to assess response. 1

If Rosacea is More Likely (No Systemic Symptoms)

• Systemic antibiotics such as tetracycline or doxycycline are first-line for papulopustular rosacea with significant erythema. 4
• Topical metronidazole can be added for maintenance. 4
• Brimonidine 0.33% topical gel is the only FDA-approved treatment specifically for facial erythema of rosacea. 5

If Drug Reaction or Erythema Multiforme is Suspected

• Discontinue any potentially causative medications immediately. 1
• High-potency topical corticosteroids (avoiding face where low-potency hydrocortisone should be used) for limited involvement. 1, 6
• Systemic corticosteroids (methylprednisolone 0.5-1 mg/kg/day) if there is extensive involvement or mucosal lesions. 1
• Admit to hospital if there is any mucosal involvement, blistering >10% body surface area, or signs of Stevens-Johnson syndrome/toxic epidermal necrolysis. 1

Critical Pitfalls to Avoid

• Do not delay doxycycline if tickborne disease is suspected - waiting for serologic confirmation can result in progression to severe disease with CNS involvement, renal failure, or death. 1
• Do not assume normal absolute monocytes rule out pathology - relative monocytosis indicates a shift in the differential that may reflect early infection or other process. 1
• Do not miss Mycoplasma pneumoniae - this requires specific antibiotic coverage (macrolides or fluoroquinolones) rather than doxycycline alone. 2
• Do not apply topical corticosteroids to undiagnosed facial erythema without ruling out infectious causes, as this can worsen certain conditions. 1
• Do not use systemic corticosteroids empirically without establishing whether this is an infectious versus inflammatory process, as steroids can worsen tickborne diseases. 1

Monitoring and Follow-Up

• Reassess within 24-48 hours if empiric doxycycline is started for suspected tickborne disease - symptoms should begin improving within 1 week. 1
• Serial clinical photography to document progression or improvement of facial erythema. 1
• Repeat complete blood count to monitor for resolution of relative monocytosis and development of any cytopenias. 1
• Convalescent serology at 2-4 weeks after symptom onset to confirm diagnosis of tickborne disease. 1