Differential Diagnosis: Burning Pain in the Right Big Toe with Crepitus

1. Hallux Rigidus (Degenerative Osteoarthritis of MTP1) ⭐ Most Likely

• Painful condition of the hallux MTP joint characterised by loss of motion (especially dorsiflexion) and osteophyte formation on the dorsum and sides of the joint — Bailey & Love's Surgery, 28th Ed
• Crepitus arises from irregular articular cartilage and dorsal osteophytes grinding during movement
• Pain is worse with push-off during walking, often described as burning/aching
• May affect adolescents (osteochondrosis aetiology) or adults (post-traumatic, idiopathic)
• X-ray: joint space narrowing, subchondral sclerosis, subchondral cysts, dorsal osteophytes — THIEME Atlas of Anatomy
• Grading (Coughlin & Shurnas): Grade 0–4 based on dorsiflexion range and radiographic changes

2. Gout (Podagra)

• The first MTP joint is the most common site of initial gout involvement — Harrison's Principles of Internal Medicine 22E
• Podagra: acute monoarthritis of MTP1 with severe pain, swelling, erythema, warmth
• Classically nocturnal onset; pain develops over 6–12 hours
• Burning/throbbing quality is characteristic
• Crepitus in chronic gout from intra-articular tophi and articular damage
• Serum uric acid may be normal in 30% of acute attacks — do not use to exclude
• Diagnosis: joint aspiration showing needle-shaped, negatively birefringent monosodium urate crystals
• Imaging: double-contour sign on ultrasound; "rat-bite" erosions with overhanging edges on X-ray — Imaging Anatomy, THIEME

3. Sesamoiditis / Sesamoid Stress Fracture

• Pain localised to the plantar surface of the MTP1 (under the first metatarsal head)
• Common in athletes/runners; chronic repetitive loading
• Sesamoiditis presents with tenderness directly beneath the hallux MTP joint
• Must be differentiated from sesamoid fracture, bipartite sesamoid, and hallux rigidus — Rockwood & Green's Fractures in Adults, 10th Ed
• Crepitus can occur with sesamoid fragmentation or fibrocartilaginous degeneration
• Medial sesamoid most frequently involved

4. Turf Toe / MTP1 Plantar Plate Injury

• Plantar plate disruption from hyperextension at MTP1
• Burning pain on weight-bearing, especially push-off
• Crepitus with associated synovitis or sesamoid involvement
• Common in athletes on artificial turf; low-grade injuries managed non-operatively, high-grade require reconstruction — Bailey & Love's, 28th Ed

5. Morton's Neuroma (Interdigital Neuroma)

• Perineural fibrosis of the intermetatarsal plantar digital nerve
• Classically involves 2nd–3rd or 3rd–4th interspace, but can affect 1st–2nd
• Lancinating, burning pain radiating to the toes; paresthesia; worsened by tight footwear
• Crepitus or a nodule may be palpable — Rosen's Emergency Medicine
• Positive Mulder's click (compression of metatarsal heads reproduces pain)
• MRI is the diagnostic modality of choice

6. Rheumatoid Arthritis / Psoriatic Arthritis / Reactive Arthritis

• Inflammatory polyarthritides can present as MTP1 monoarthritis initially
• RA: symmetric small joint involvement; morning stiffness >1 hour; RF/anti-CCP positive
• Psoriatic arthritis: dactylitis ("sausage toe"), enthesitis, skin/nail changes; can affect a single ray
• Reactive arthritis: triad of arthritis, urethritis, conjunctivitis; post-infectious (Chlamydia, enteric pathogens)
• Crepitus from synovial hypertrophy and cartilage erosion

7. Pseudogout (Calcium Pyrophosphate Deposition, CPPD)

• Calcium pyrophosphate crystals; less predilection for MTP1 than gout but possible
• Crystals are rhomboid-shaped, positively birefringent (yellow when perpendicular to light source)
• Joint aspiration distinguishes from gout

8. Complex Regional Pain Syndrome (CRPS)

• Burning pain disproportionate to any inciting event; often post-traumatic
• CRPS Type I (no nerve lesion) or Type II (with nerve lesion)
• Associated vasomotor changes (skin colour, temperature), sudomotor changes (sweating/oedema), and trophic changes
• Diagnosed using the Budapest Criteria (sensory, vasomotor, sudomotor/oedema, motor/trophic) — Rosen's Emergency Medicine

9. Peripheral Neuropathy

• Burning pain beginning in the toes and soles; typically bilateral and symmetric
• Causes: diabetic neuropathy, HIV neuropathy, B12 deficiency, alcohol, chemotherapy
• Burning predominantly sensory; crepitus would suggest a concurrent mechanical cause
• Distal numbness, tingling, and burning pain beginning in the feet — Harrison's, 22E

10. Erythromelalgia

• Rare; episodic burning pain, redness, and warmth of the extremities (often toes/feet)
• Triggered by warmth; relieved by cooling/elevation
• Primary (mutations in SCN9A) or secondary (myeloproliferative disorders, diabetes)
• No crepitus; burning is the cardinal symptom

Rare / Not-To-Miss Causes

Diagnostic Approach Summary

Burning toe pain + Crepitus
         │
         ├── Dorsal pain + stiffness + restricted ROM → Hallux Rigidus (X-ray)
         ├── Acute, severe, nocturnal, erythema → Gout (aspiration + crystals)
         ├── Plantar pain, athlete/runner → Sesamoiditis (MRI/bone scan)
         ├── Post-hyperextension injury → Turf Toe (MRI)
         ├── Burning + radiation to toes, nodule → Morton's Neuroma (MRI)
         ├── Polyarthritis, morning stiffness → RA/SpA (RF, anti-CCP, HLA-B27)
         ├── Post-traumatic burning, skin changes → CRPS (Budapest criteria)
         └── Bilateral burning + numbness → Peripheral neuropathy (EMG/NCS)