What are the differential diagnoses and management options for tender and bruised lumps in the legs?

Differential Diagnoses for Tender and Bruised Lumps in the Legs

The most critical first step is to exclude deep vein thrombosis (DVT) using proximal compression ultrasound, as this represents a life-threatening condition requiring immediate anticoagulation. 1, 2, 3

Immediate Priority: Rule Out DVT

Before attributing leg lumps to benign causes, DVT must be excluded, particularly when risk factors are present (recent immobilization, surgery, pregnancy, cancer, or previous DVT history). 2, 3

DVT Diagnostic Algorithm:

• Perform proximal compression ultrasound (CUS) of the common femoral and popliteal veins as the initial test 1, 3
• If CUS is positive: initiate DVT treatment immediately without confirmatory venography 1, 3
• If CUS is negative: perform D-dimer testing; if D-dimer is negative, no further testing is needed 1, 3
• Consider whole-leg ultrasound in patients unable to return for serial testing or with severe calf symptoms 1, 3

Primary Differential Diagnoses

1. Deep Muscle Contusion/Hematoma

• Results from direct trauma (blow or fall) causing muscle fiber tearing with subsequent bleeding into tissue 4
• Presents with localized tenderness, swelling, and ecchymosis (bruising) 4
• Management: PRICE protocol (Protection, Rest, Ice, Compression, Elevation) with NSAIDs for pain and swelling reduction 2

2. Erythema Nodosum

• Most common inflammatory cause of tender leg nodules (84.4% of inflammatory cases) 5
• Presents as tender, erythematous nodules typically on lower legs 5
• Clinical clues: female sex (OR 6.43) and lower leg involvement (OR 7.14) 5
• Treatment: colchicine is preferred when erythema nodosum is the dominant lesion 1

3. Subcutaneous Panniculitis-like T-cell Lymphoma

• Presents as solitary or multiple subcutaneous nodules to indurated plaque-like lesions 1
• Often has a "bruise-like aspect" with CD4+/CD56+ phenotype 1
• Requires biopsy for definitive diagnosis with immunophenotyping 1

4. Venous Claudication/Post-thrombotic Syndrome

• Presents with tight, bursting pain in entire leg, worse in calf 1
• Associated with edema and signs of venous stasis 1
• History of iliofemoral DVT is characteristic 1
• Subsides slowly with rest and improves with leg elevation 1

5. Symptomatic Baker's Cyst

• Swelling and tenderness behind knee extending down calf 1
• Pain present both with exercise and at rest 1
• Not intermittent in nature 1

6. Infectious Causes (5.8% of cases)

• Include fungal infections (Acremonium, Penicillium), atypical mycobacteria (M. abscessus, M. fortuitum), or M. leprae 5
• Requires tissue culture and histopathology for diagnosis 5

7. Cutaneous Lymphomas

• Primary cutaneous diffuse large B-cell lymphoma (leg type) presents as red to bluish-red tumors, particularly in elderly patients on legs 1
• Biopsy essential showing CD20+, CD79a+, BCL2+, BCL6+, MUM-1+, FoxP1+ 1

Diagnostic Approach

Clinical Evaluation Must Include:

• Vascular assessment: palpate femoral, popliteal, dorsalis pedis, and posterior tibial pulses 1
• Skin examination: look for elevation pallor/dependent rubor, asymmetric hair growth, nail bed changes, calf muscle atrophy 1
• Trauma history: mechanism of injury, timing, progression of symptoms 4
• Systemic symptoms: fever, weight loss, night sweats (suggesting lymphoma or infection) 1, 5

Diagnostic Testing Algorithm:

1. First: Proximal CUS to exclude DVT 1, 3
2. If DVT excluded and trauma history present: treat as muscle contusion with PRICE protocol 2
3. If no clear trauma or atypical presentation: obtain biopsy for histopathology and immunophenotyping 1, 5
4. If infection suspected: tissue culture in addition to histopathology 5

Critical Pitfalls to Avoid

• Never assume "just a bruise" without excluding DVT when swelling seems disproportionate to injury mechanism 2
• Female patients with lower leg nodules have high probability of inflammatory causes (particularly erythema nodosum), but biopsy is still crucial for definitive diagnosis 5
• Bruise-like appearance can represent hematologic malignancy (CD4+/CD56+ hematodermic neoplasm or lymphoma) requiring urgent biopsy 1
• Leg ulcers in patients with tender lumps may indicate vasculitis, requiring systemic treatment rather than local measures 1