What is the diagnosis and management for a 31-year-old male with a pinpoint rash (erythematous base) on his lower legs and mid torso, joint pain in his neck and knees, slightly low white blood cell (WBC) count, elevated lymphocytes, monocytes, and basophils, and normal hemoglobin (Hgb), liver function, and electrolytes, who also takes non-prescribed testosterone injections and presented with a headache and nausea 5 days prior to the onset of the rash?

Diagnosis: Likely Viral Exanthem with Possible Tickborne Rickettsial Disease Consideration

This patient most likely has a viral exanthem given the prodromal symptoms, ascending pinpoint rash with erythematous base, lymphocytic predominance on CBC, and absence of fever or tick exposure, but Rocky Mountain Spotted Fever (RMSF) or ehrlichiosis must be empirically treated with doxycycline if clinical suspicion exists, as delay in treatment significantly increases mortality. 1

Differential Diagnosis Priority

Primary Consideration: Viral Exanthem

• The clinical presentation of headache and nausea followed 2.5 days later by an ascending pinpoint rash with erythematous base, combined with slightly elevated lymphocytes, monocytes, and basophils with slightly low WBC, strongly suggests a viral etiology 1
• The absence of fever at presentation and normal platelets argue against severe bacterial infection 1
• Common viral causes include enteroviral infections, human parvovirus B19, human herpesvirus 6, and Epstein-Barr virus, all of which can present with maculopapular rashes and constitutional symptoms 1

Critical Exclusion: Tickborne Rickettsial Disease

• Despite no reported tick exposure, RMSF and ehrlichiosis must remain in the differential because up to 40% of patients do not recall a tick bite 1
• The ascending rash pattern starting on lower legs is consistent with RMSF, which classically begins on wrists and ankles before spreading centrally 1
• However, several features argue against RMSF: absence of fever at presentation (though fever may be absent early), normal platelets (thrombocytopenia is common in RMSF), and normal liver function (transaminase elevation typical in RMSF) 1
• The slightly elevated lymphocytes favor viral etiology over RMSF, which typically shows neutrophil predominance 1
• Ehrlichiosis presents with rash in only one-third of adults (though up to 66% in children), making the prominent rash less consistent with this diagnosis 1

Testosterone-Related Considerations

• The patient's use of non-prescribed intramuscular testosterone injections can cause local injection site reactions including erythema, swelling, and nodules, but these are localized rather than systemic 1, 2
• Transdermal testosterone preparations cause erythema or pruritus in up to 66% with patches and 5% with gels, but the patient is using injections 1
• Testosterone therapy does not typically cause systemic rash patterns as described 1, 2

Management Algorithm

Immediate Actions

1. If any clinical concern for RMSF or ehrlichiosis exists (endemic area, outdoor exposure, severe headache, joint pain), initiate doxycycline 100 mg twice daily immediately without waiting for confirmatory testing 1

   • The classic petechial rash of RMSF typically appears on day 5-6 of illness, and this patient is within that timeframe 1
   • Treatment delay beyond day 5 significantly increases mortality risk 1
   • Doxycycline is the treatment of choice for all ages and should not be withheld even in the absence of confirmed tick exposure 1

2. Obtain serologic testing for RMSF and ehrlichiosis (IgM and IgG) with acute and convalescent titers 2-4 weeks apart 1

   • PCR testing if available can provide earlier diagnosis 1
   • Initial serology is often negative early in disease course 1

3. Perform peripheral blood smear examination looking for intracellular morulae (suggestive of ehrlichiosis) 1

Supportive Management

• Symptomatic treatment with antihistamines for pruritus 1
• Adequate hydration and analgesics for headache and joint pain 1
• Monitor for development of fever, worsening rash, or systemic symptoms 1

Testosterone Management Considerations

• Counsel patient on risks of non-prescribed testosterone use, including lack of monitoring for polycythemia (which can occur in 3-44% depending on formulation), hepatotoxicity with oral preparations, and cardiovascular risks 1, 2, 3
• Baseline monitoring should include PSA, hematocrit/hemoglobin, and digital rectal examination if testosterone use continues 1
• The slightly low WBC and elevated monocytes are not typical complications of testosterone therapy 1, 2

Follow-Up Protocol

If Viral Etiology Confirmed (RMSF/Ehrlichiosis Ruled Out)

• Expectant management with symptom resolution typically within 7-14 days 1
• No specific antiviral therapy required for most viral exanthems 1
• Return precautions for development of fever, petechial rash, altered mental status, or worsening symptoms 1

If Empiric Doxycycline Started

• Continue doxycycline for minimum 7 days and at least 3 days after fever resolves 1
• Clinical improvement typically occurs within 24-48 hours if rickettsial disease present 1
• Lack of improvement within 48-72 hours suggests alternative diagnosis 1

Critical Pitfalls to Avoid

• Never delay doxycycline treatment while awaiting confirmatory testing if RMSF is suspected, as mortality increases significantly with delayed treatment 1
• Do not rely on absence of tick bite history to exclude tickborne disease—up to 40% of patients do not recall exposure 1
• Do not wait for the classic petechial rash or palm/sole involvement to diagnose RMSF, as these are late findings indicating disease progression 1
• The absence of fever does not exclude early RMSF, as fever patterns can be variable 1
• Normal platelet count does not exclude rickettsial disease, though thrombocytopenia is common 1