X-ray is the Next Investigation
Plain radiographs in two orthogonal planes should always be the first investigation for an elderly male with a well-demarcated, red, painful thigh lesion, as they rapidly identify bone destruction, periosteal reaction, soft tissue calcification, or gas formation that would indicate deeper pathology requiring urgent specialized referral. 1
Why X-ray Takes Priority
The clinical presentation—a painful, well-demarcated red lesion in an elderly patient—could represent superficial cellulitis, but the critical principle is to never assume superficial appearance means superficial disease. 1 This lesion could represent:
- Overlying cellulitis from underlying osteomyelitis 1
- A bone tumor breaking through the cortex 1
- Soft tissue infection with gas formation
- Deep tissue pathology masquerading as a superficial process
Plain radiographs are rapid, inexpensive, and provide critical information about whether deeper structures are involved, making them mandatory before any other diagnostic step. 1
The Fundamental Principle: Never Biopsy Before Imaging
Punch biopsy should not be performed before adequate imaging, as it can contaminate tissue planes and compromise future surgical management if malignancy is present. 1 This is a high-level evidence recommendation that applies universally to suspected bone or deep tissue pathology. 2, 1
If a bone sarcoma or aggressive lesion is present, an improperly placed biopsy tract must be excised en bloc with the definitive resection specimen to prevent local recurrence. 2 Performing biopsy first would:
- Contaminate multiple tissue compartments 2
- Compromise limb-salvage surgery options 2
- Require removal of the entire biopsy tract later 2
Why Not the Other Options First
USG (ultrasound) has no established role as a first-line investigation for this presentation in major guidelines. While ultrasound can guide biopsies later, it does not provide the comprehensive bone and soft tissue assessment needed initially. 2, 1
MRI is indicated only when malignancy cannot be excluded with certainty on plain radiographs. 1 It is the next step after X-ray if bone sarcoma or deep soft tissue pathology is suspected, serving as the best modality for local staging of the whole bone with adjacent joints. 2, 1 Ordering MRI first wastes time and resources when X-ray may immediately clarify the diagnosis.
Clinical Algorithm After X-ray
If X-ray shows normal findings with persistent symptoms:
- Proceed to MRI to evaluate soft tissue and bone marrow 1
- Consider treating as soft tissue infection for 2 weeks if diabetic foot infection suspected, then repeat X-ray 2
If X-ray shows suspicious bone lesion:
- Obtain MRI of the whole bone with adjacent joints for staging 2, 1
- Refer to a specialized bone sarcoma center before any biopsy 2, 1
- The biopsy must be performed at the facility providing definitive surgical management 2
If X-ray shows classic osteomyelitis changes (cortical erosion, periosteal reaction, mixed lucency and sclerosis):
- Treat for presumptive osteomyelitis after obtaining appropriate specimens for culture 2
Critical Pitfalls to Avoid
Do not assume age rules out malignancy: While metastatic disease and multiple myeloma are more common in elderly patients than primary bone sarcomas, aggressive lesions still require proper workup. 3
Do not delay imaging for empirical antibiotic treatment: Even if cellulitis seems likely, persistent or night pain warrants radiological assessment to exclude bone pathology. 1
Do not perform excision biopsy if there is any possibility of an aggressive-benign or malignant lesion, as this contaminates tissue compartments unnecessarily. 2, 4
Answer: C. X-ray