What is the most likely diagnosis and recommended course of action for a patient with a rapidly growing groin lymph node, new lymph node growth behind the ear, fatigue, pruritus, and lower back pain, and a history of a normal low-dose kidney stone protocol CT scan?

Lymphoma is the Most Likely Diagnosis Requiring Urgent Excisional Lymph Node Biopsy

This clinical presentation strongly suggests lymphoma and requires immediate excisional lymph node biopsy for definitive diagnosis, followed by comprehensive staging and prompt treatment initiation. The constellation of rapidly growing lymphadenopathy in multiple sites (groin and post-auricular), constitutional symptoms (fatigue requiring excessive sleep), pruritus with skin changes, and new-onset lower back/hip pain radiating to legs is highly concerning for malignant lymphoproliferative disease.

Clinical Features Strongly Suggesting Lymphoma

Lymph Node Characteristics

• The groin lymph node measuring 2.7 cm with rubbery, fixed consistency is highly suspicious for malignancy 1, 2
• Lymph nodes larger than 2 cm, particularly when hard or fixed to surrounding structures, strongly indicate malignancy or granulomatous disease 1
• The rapid initial growth followed by stability is characteristic of aggressive lymphoma behavior 2
• Multiple site involvement (groin plus post-auricular) suggests systemic disease rather than localized infection 1, 3

Constitutional Symptoms (B Symptoms)

• The combination of severe fatigue requiring 7-10 hours of sleep plus 2-4 hour naps, along with pruritus, constitutes concerning systemic symptoms 4, 5
• While pruritus and fatigue are not classified as formal B symptoms, they are common in lymphoma patients and indicate systemic involvement 4
• These symptoms mandate treatment initiation in follicular lymphoma even without other high tumor burden criteria 4

Concerning Additional Features

• The new lower back pain radiating to hips and legs raises concern for bone marrow involvement or retroperitoneal lymphadenopathy 6, 7
• The scaly rash with small bumps could represent cutaneous involvement or paraneoplastic manifestations 5

Immediate Diagnostic Workup Required

Tissue Diagnosis (Most Critical)

• Excisional lymph node biopsy of the groin node is mandatory and should be performed urgently 6, 7
• The post-auricular node provides an alternative accessible site if groin biopsy is technically difficult 8
• Core needle biopsy is inadequate for proper lymphoma diagnosis and should only be used when excisional biopsy is impossible 6
• Fine-needle aspiration alone is insufficient except in rare emergency situations requiring immediate treatment 6
• Tissue must provide adequate material for fresh-frozen and formalin-fixed samples for comprehensive analysis including immunohistochemistry (CD3, CD15, CD20, CD30, CD45, CD79a, PAX5), flow cytometry, and molecular studies 6, 7

Essential Laboratory Studies

• Complete blood count with differential to assess for cytopenias or leukocytosis 6, 7
• Comprehensive metabolic panel including liver and kidney function 6, 7
• Lactate dehydrogenase (LDH) and uric acid as tumor burden markers and for prognostic purposes 6, 7
• HIV, hepatitis B, and hepatitis C screening (mandatory before treatment) 6, 4
• Serum protein electrophoresis for B-cell lymphomas 6

Imaging Studies

• PET/CT from skull base to mid-thigh is the gold standard for staging and must be performed 6, 4, 7
• The normal kidney stone CT from an unspecified time ago is inadequate for lymphoma evaluation 6
• Contrast-enhanced diagnostic CT of neck, chest, abdomen, and pelvis if PET/CT is not immediately available 6
• Given the lower back/hip pain, bone marrow biopsy should be performed if PET scan shows multifocal (≥3) skeletal lesions 6

Additional Staging Procedures

• Bone marrow biopsy is not routinely required if PET scan is negative or shows homogenous uptake, but should be performed if cytopenias are present or PET shows multifocal skeletal involvement 6
• Diagnostic lumbar puncture with prophylactic intrathecal chemotherapy should be strongly considered given the concerning neurologic symptoms (back/hip/leg pain) 6

Differential Diagnosis Considerations

Most Likely: Aggressive Lymphoma

• Hodgkin lymphoma presents with B symptoms, lymphadenopathy, fatigue, and pruritus 4, 5, 2
• Diffuse large B-cell lymphoma commonly manifests with rapidly growing lymphadenopathy and constitutional symptoms 6, 5, 2
• Follicular lymphoma can present with multiple site involvement and systemic symptoms 6, 4

Less Likely but Must Exclude

• Tuberculosis must be excluded, particularly given the constitutional symptoms, though multiple lymph node sites and rapid growth are less typical 5, 1
• HIV-associated lymphoproliferative disorders require HIV testing 6
• Metastatic carcinoma is possible but less likely given the age-typical presentation and symptom constellation 1

Critical Pitfalls to Avoid

• Do not delay biopsy waiting for additional imaging or laboratory results 6, 7
• Do not accept fine-needle aspiration or core needle biopsy as adequate for initial diagnosis 6
• Do not dismiss the lower back pain as musculoskeletal without imaging evaluation for bone/marrow involvement 6
• Do not start empiric antibiotics or corticosteroids before obtaining tissue diagnosis, as corticosteroids can mask lymphoma histology 1
• Do not assume the previous normal CT excludes current malignancy, as lymphoma can develop rapidly 2

Disposition and Urgency

• Hematology/oncology consultation should be obtained immediately 7
• Admission should be considered if B symptoms are affecting functional status or if there is concern for tumor lysis syndrome given the rapid growth 7
• Excisional biopsy should be scheduled within 48-72 hours maximum 6, 7
• If biopsy confirms lymphoma, treatment initiation should not be delayed, as the presence of systemic symptoms mandates immediate therapy regardless of stage 6, 4