Pruritus on Forearms with Skin Bruising: Workup and Management
You must immediately obtain a complete blood count (CBC) with blood film, ferritin level, and lactate dehydrogenase (LDH) to rule out potentially life-threatening hematological causes, particularly polycythemia vera and lymphoma, which can present with pruritus and bruising. 1
Initial Diagnostic Approach
The combination of pruritus and bruising on the forearms raises serious concern for underlying hematological disorders that directly impact mortality. Here's the algorithmic workup:
Essential First-Line Laboratory Tests
Order these immediately:
- CBC with differential and blood film - Look specifically for elevated hemoglobin/hematocrit, elevated platelets, elevated white cells, or abnormal lymphocytes 1
- Ferritin level - Both iron deficiency AND iron overload can cause pruritus 1
- LDH - Elevated in lymphoproliferative disorders 1
- ESR - Characteristically LOW in polycythemia vera 1
Critical Red Flags in History
Ask specifically about:
- Aquagenic pruritus (intense itching after water contact) - highly characteristic of polycythemia vera 1
- Night sweats, fevers, weight loss - suggests lymphoma 1
- Microcytosis with elevated hemoglobin - suggests polycythemia vera with secondary iron deficiency from increased red cell production 1
Interpretation and Next Steps
If CBC Shows Elevated Hemoglobin/Hematocrit:
Immediately test for JAK2 V617F mutation (present in up to 97% of polycythemia vera cases) 1. If positive, refer urgently to hematology. Polycythemia vera is a myeloproliferative neoplasm that increases thrombotic risk and can transform to acute leukemia - this directly impacts mortality.
If JAK2 negative, investigate secondary causes:
- Renal function tests
- Liver function tests
- Serum erythropoietin level
- Oxygen saturation
- Chest X-ray
- Abdominal ultrasound 1
If Lymphocytosis or Abnormal Cells Present:
Refer immediately to hematology for potential lymph node biopsy or bone marrow examination. Hodgkin lymphoma classically presents with pruritus (though bruising is less typical unless there's bone marrow involvement or thrombocytopenia) 1.
If Iron Studies Abnormal:
- Low ferritin (<15-25 μg/L): Check tissue transglutaminase antibodies for celiac disease (assuming no gluten exclusion for 6+ weeks) 1
- High ferritin: Check liver function tests to evaluate for hemochromatosis or liver disease 1
Consider Neuropathic Causes
Given the forearm location specifically, consider brachioradial pruritus - a neuropathic condition affecting the C5-C6 dermatome distribution on the dorsolateral forearms 2, 3, 4, 5. This is particularly relevant if:
- Pruritus is localized to the brachioradialis muscle distribution
- Patient has neck pain or cervical spine disease history
- Patient has chronic sun exposure history 5
If neuropathic pruritus suspected: Obtain cervical spine MRI to evaluate for disc protrusion or spinal stenosis at C5-C6 level 3, 4. Surgical decompression has been curative in refractory cases 3, 4.
Management Based on Etiology
For Polycythemia Vera-Associated Pruritus:
- Aspirin 300 mg daily - shown effective for pruritus relief 1
- Cytoreductive therapy (phlebotomy or medications)
- Consider SSRIs, phototherapy (PUVA/UVB), cimetidine, or atenolol for refractory cases 1
- Ruxolitinib (JAK1/JAK2 inhibitor) produces rapid pruritus reduction in RCTs 1
For Lymphoma-Associated Pruritus:
- Definitive treatment of lymphoma resolves pruritus 1
- Symptomatic relief: high-dose oral corticosteroids 1
- Alternative agents: cimetidine, gabapentin, carbamazepine, mirtazapine, or phototherapy 1
For Brachioradial Pruritus:
- Pregabalin as first-line medication 2
- Consider combination therapy with ketamine/amitriptyline/lidocaine cream for refractory cases 2
- Cervical spine surgery (anterior cervical discectomy and fusion) if conservative treatment fails and imaging confirms nerve compression 3, 4
Critical Pitfall to Avoid
Do not dismiss pruritus with bruising as a benign dermatological condition. The bruising component suggests either a platelet disorder, coagulation abnormality, or vascular fragility - all of which can be associated with serious hematological malignancies. Haematological causes account for approximately 2% of generalized pruritus cases, but when present with bruising, the index of suspicion must be significantly higher 1.
The British Association of Dermatologists explicitly recommends that patients with generalized pruritus and suspicion of hematological involvement receive comprehensive blood work as outlined above 1. The presence of bruising elevates this from routine screening to urgent investigation.