Diagnosis: Pityriasis Rosea
This clinical presentation is most consistent with pityriasis rosea (PR), a self-limited papulosquamous dermatosis characterized by the Christmas tree distribution pattern on the back, though the concurrent anemia and elevated alkaline phosphatase require additional investigation to exclude systemic disease. 1, 2, 3
Clinical Features Supporting Pityriasis Rosea
Christmas tree distribution pattern on the back is pathognomonic for PR, where oval erythematous lesions align along Langer's lines of cleavage 1, 2, 3
Pruritus is present in the majority of PR cases, though severity varies from mild to moderate 3
Hyperpigmented lesions can occur in PR, particularly in darker skin types or as post-inflammatory changes 2, 3
The typical course is 6-8 weeks duration with spontaneous resolution 3
Critical Diagnostic Considerations
The anemia and elevated alkaline phosphatase are NOT typical features of pityriasis rosea and warrant separate investigation. 4
Elevated Alkaline Phosphatase Differential:
Sarcoidosis can present with pruritus, hyperpigmented skin lesions, anemia, and elevated alkaline phosphatase (occurs in 10-13% of cases with hypercalcemia) 4
- However, sarcoid skin lesions typically appear as "strawberry skin" with pale granulomas on erythematous mucosa, not in Christmas tree pattern 4
Polycythemia vera causes pruritus and elevated alkaline phosphatase, but presents with elevated hemoglobin rather than anemia 4
Bladder or other malignancy may cause elevated alkaline phosphatase and should prompt bone scan if persistently elevated 4
Anemia Considerations:
Iron deficiency anemia has been correlated with pruritus in some conditions, though not specifically PR 4
Microcytic anemia with elevated alkaline phosphatase could suggest chronic disease or rare genetic disorders of iron metabolism 4
Recommended Diagnostic Workup
Initial laboratory testing should include:
- Complete blood count with differential to characterize the anemia 5
- Comprehensive metabolic panel including calcium, phosphate, and liver function tests 4
- Serum angiotensin-converting enzyme (ACE) level if sarcoidosis suspected (elevated in 60-83% of cases) 4
- Chest X-ray to evaluate for pulmonary sarcoidosis or other systemic disease 4
Skin biopsy should be performed if:
- Diagnosis remains uncertain after initial evaluation 6
- Lesions persist beyond 8-12 weeks 3
- Systemic symptoms suggest alternative diagnosis 2
Management Approach
For Pityriasis Rosea:
Reassurance and symptomatic treatment suffice for the vast majority of cases. 3
- Topical emollients for xerosis and barrier repair 4
- Topical corticosteroids (mild-moderate potency) for pruritus control 5
- Oral antihistamines (cetirizine 10 mg daily or similar) for moderate pruritus 4
Active intervention with oral acyclovir (800 mg five times daily for 7 days) may shorten disease duration if started within the first week of eruption 3
Alternative treatments for severe pruritus:
For Concurrent Laboratory Abnormalities:
The elevated alkaline phosphatase requires:
- Bone scan if persistently elevated to exclude metastatic disease 4
- Further evaluation for sarcoidosis if ACE elevated or chest X-ray abnormal 4
The anemia requires:
Important Caveats
PR in pregnancy requires active management due to potential fetal complications; consider early acyclovir therapy 2, 3
Atypical presentations without herald patch or with unusual distribution may require biopsy to exclude secondary syphilis, drug eruption, or other papulosquamous disorders 2, 3
Persistent lesions beyond 12 weeks should prompt reconsideration of diagnosis and skin biopsy 3
The combination of PR-like rash with systemic findings (anemia, elevated alkaline phosphatase) is unusual and mandates thorough investigation for underlying systemic disease, particularly sarcoidosis or malignancy 4