What is the next investigation for a well-demarcated, red, painful lesion on the thigh?

X-ray is the Next Investigation

For a well-demarcated, red, painful lesion on the thigh, plain radiographs in two planes should always be the first investigation before any biopsy is performed. 1, 2

Why X-ray First: The Critical Algorithmic Approach

Rule Out Deep Pathology Before Tissue Sampling

• Plain X-ray is mandatory as the initial imaging because pain (especially persistent pain) warrants radiological assessment to exclude bone involvement, osteomyelitis, or bone tumors that may present with overlying soft tissue changes 1, 2

• Never biopsy before imaging - this is a fundamental principle that prevents tissue contamination and allows proper surgical planning if malignancy is discovered 1, 2

• The presence of a red, painful lesion does not guarantee superficial disease; it could represent overlying cellulitis from underlying osteomyelitis or a bone tumor breaking through the cortex 2

What X-ray Reveals

Plain radiographs rapidly identify:

• Bone destruction or periosteal reaction 1, 2
• Soft tissue calcification or gas formation 2
• Cortical involvement that would change management entirely 1

The Sequencing Matters for Patient Outcomes

If you perform punch biopsy first (Option A):

• You contaminate tissue planes, compromising future surgical management if malignancy is present 1, 2
• You miss underlying bone pathology that requires specialized referral 1, 2
• Diagnostic shave or punch biopsies can lead to incorrect diagnosis due to sampling error 1

The correct algorithm is:

1. X-ray first (two planes) 1, 2
2. If X-ray normal but symptoms persist → MRI for soft tissue evaluation 2
3. If X-ray shows suspicious bone lesion → MRI of whole bone with adjacent joints, then referral to specialized center before biopsy 1, 2
4. Only after imaging excludes deep pathology → consider punch biopsy for superficial dermatologic diagnosis 1, 3

Why Not the Other Options Initially

• MRI (Option B) is indicated only when malignancy cannot be excluded with certainty on plain radiographs, making it a second-line test 1, 2

• Ultrasound (Option D) is not mentioned in guidelines as appropriate initial imaging for painful bone/soft tissue lesions with these characteristics 1, 2

• Punch biopsy (Option A) has a role in dermatologic diagnosis but only after imaging excludes deeper pathology 1, 2, 3

Common Pitfall to Avoid

The most dangerous error is assuming a superficial clinical presentation means superficial disease - pain is a red flag that demands radiological assessment before any invasive procedure 1, 2