X-ray is the Next Investigation
For a well-demarcated, red, painful thigh lesion, plain X-ray in two planes should be the first investigation to exclude bone or deep tissue pathology before considering any biopsy. 1
Rationale for X-ray First
Plain radiographs must always be the first investigation for any suspected bone or deep tissue lesion presenting with pain, as they rapidly identify bone destruction, periosteal reaction, soft tissue calcification, or gas formation that could indicate serious underlying pathology 2, 1
The presence of pain, particularly if persistent, warrants radiological assessment to exclude bone pathology such as osteomyelitis, bone tumor, or other deep tissue involvement that may present with overlying erythema 1
Never assume a superficial presentation means superficial disease - a red, painful lesion could represent overlying cellulitis from underlying osteomyelitis or a bone tumor breaking through the cortex 1
Why Not Punch Biopsy First
Punch biopsy should never be performed before adequate imaging, as it can contaminate tissue planes and compromise future surgical management if malignancy (such as bone sarcoma) is present 2, 1
The fundamental principle is to stage the lesion before biopsy, allowing proper surgical planning and choice of biopsy location if malignancy is discovered 2
Biopsy performed at the wrong time or location can spread tumor cells through tissue compartments unnecessarily, making definitive treatment more difficult 2
Algorithmic Approach After X-ray
If X-ray shows normal findings with persistent symptoms → proceed to MRI to evaluate soft tissue and bone marrow pathology 1
If X-ray shows suspicious bone lesion → obtain MRI of the whole bone with adjacent joints for staging, then refer to specialized center before any biopsy 2, 1
If X-ray definitively excludes bone/deep pathology and clinical presentation suggests purely dermatologic disease → then consider punch biopsy for full-thickness skin sampling 2, 3
Common Pitfall to Avoid
The most critical error would be performing a punch biopsy first based solely on the superficial appearance of the lesion, potentially missing underlying bone pathology and contaminating tissue planes if malignancy exists 2, 1
Answer: C. X-ray