What is the diagnosis and treatment for a patient presenting with a papulovesicular rash, an inflamed lymph node in the axillary region, and a subsequent dark brownish-greyish maculoplaque in the axillary fold?

Clinical Diagnosis: Cat Scratch Disease (Bartonella henselae Infection)

The presentation of papulovesicular rash with inflamed axillary lymphadenopathy followed by a dark brownish-greyish maculoplaque in the axillary fold is most consistent with cat scratch disease caused by Bartonella henselae. 1

Key Diagnostic Features

• The classic presentation includes a primary inoculation lesion (papule or pustule) at the site of cat scratch or bite, followed by regional lymphadenopathy developing 1-3 weeks later 1
• The initial papulovesicular rash represents the inoculation site where the organism entered through broken skin 1
• The inflamed axillary lymph node is the hallmark finding—regional lymphadenopathy occurs in the drainage basin of the inoculation site 1
• The subsequent dark brownish-greyish maculoplaque likely represents evolution of the primary lesion or a secondary skin manifestation 1

Differential Diagnosis Considerations

Why Not Other Conditions?

• Tularemia can present with axillary lymphadenitis and ulceroglandular disease, but typically shows more prominent ulceration and systemic toxicity 1
• Lymphomatoid papulosis presents with papulonodular lesions that wax and wane with spontaneous regression, but lacks the acute lymphadenitis pattern 1, 2
• Papular urticaria from arthropod bites causes symmetrically distributed pruritic papulovesicles but does not typically cause significant lymphadenopathy 3
• Granulomatous slack skin affects axillae but presents with diffusely infiltrated, later slack skin, not acute lymphadenitis 1

Diagnostic Workup

• Serological testing for Bartonella henselae is the primary diagnostic method, though cross-reactivity with B. quintana can occur 1
• Warthin-Starry silver stain of lymph node tissue (if biopsy performed) confirms diagnosis by demonstrating organisms 1
• PCR testing is available and can differentiate species 1
• Blood cultures are rarely positive due to the fastidious nature of the organism 1
• Histopathology of affected lymph nodes shows granulomatous inflammation with suppurative features 4

Critical History Elements

• Exposure to cats, particularly kittens, is essential to elicit 1
• Scratches or bites from cats typically precede symptoms by 1-3 weeks 1
• The axillary location suggests upper extremity inoculation site 4

Treatment Recommendations

Azithromycin is the treatment of choice based on the only double-blind, placebo-controlled trial demonstrating 80% regression of lymph node size at 30 days (P = 0.02). 1

Specific Dosing Regimen

• For patients weighing ≥45.5 kg (100 lb): azithromycin 500 mg orally on day 1, then 250 mg once daily for 4 additional days 1
• For patients weighing <45.5 kg: azithromycin 10 mg/kg orally on day 1, then 5 mg/kg once daily on days 2-5 1

Expected Clinical Course

• Antimicrobial treatment has shown variable but rarely dramatic results 1
• Most cases are self-limited, with lymphadenopathy resolving over weeks to months even without treatment 1
• Treatment likely hastens resolution and may prevent suppurative complications 1

Important Clinical Pitfalls

• Do not confuse with bacillary angiomatosis, which occurs in immunocompromised patients (particularly AIDS) and presents as red papules or subcutaneous nodules, not primarily as lymphadenitis 1
• The dark maculoplaque may be mistaken for a malignant process—clinical context and lymph node involvement help differentiate 5
• Needle aspiration of suppurative lymph nodes may be necessary for symptomatic relief but should be performed carefully to avoid fistula formation 1
• Excisional biopsy of lymph nodes is generally not recommended unless diagnosis is uncertain or malignancy cannot be excluded 1

When to Seek Expert Consultation

• Atypical presentations involving CNS, eye, or visceral organs require specialist involvement 1
• Immunocompromised patients may develop disseminated disease requiring prolonged therapy 1
• Failure to respond to azithromycin within 2-4 weeks warrants reassessment of diagnosis 1