Provisional Diagnosis: Morton's Neuroma (Interdigital Neuroma)
The most likely provisional diagnosis for pain over the 4th MTP joint with tingling is Morton's neuroma, an interdigital neuroma typically occurring between the 3rd and 4th metatarsal heads that causes both localized pain and neuritic symptoms including tingling.
Clinical Reasoning
The combination of localized MTP pain with tingling is the key distinguishing feature here. While several conditions cause MTP joint pain, the addition of tingling/neuritic symptoms points specifically toward nerve involvement rather than pure joint pathology.
Why Morton's Neuroma is Most Likely:
- Tingling is pathognomonic for nerve irritation/compression, not typical of pure synovitis or joint instability
- The 4th MTP region corresponds to the 3rd-4th intermetatarsal space, the second most common location for Morton's neuroma (after the 2nd-3rd space)
- Research demonstrates that MTP synovitis can cause "irritation of the common digital nerve" with associated neuritic symptoms 1
- The intermetatarsal nerve compression produces both pain radiating to the MTP joint and tingling in adjacent toes
Differential Considerations
MTP Joint Synovitis
While monarticular synovitis of lesser MTP joints is well-documented 1, 2, 3, it typically presents with:
- Joint thickening and warmth
- Decreased range of motion
- Positive drawer test (instability)
- Absence of tingling unless secondary nerve compression occurs
The research shows synovitis can cause "evidence of irritation of the common digital nerve" 1, but this is a secondary phenomenon, not the primary pathology when tingling is prominent.
MTP Instability
Lesser MTP instability 3 presents with:
- Positive drawer test
- Progressive deformity
- Pain with dorsiflexion
- No neuritic symptoms unless advanced with nerve compression
Gout
While gout guidelines emphasize first MTP involvement 4, 5, it:
- Rarely affects the 4th MTP as an isolated site
- Presents with acute inflammatory signs (erythema, warmth, severe pain)
- Does not cause tingling
- Would require crystal confirmation for definitive diagnosis
Clinical Examination Priorities
Look specifically for:
- Mulder's click: Compression of the intermetatarsal space while manipulating the toes
- Positive Mulder's sign: Pain with side-to-side compression of metatarsal heads
- Tingling radiation into the 4th and/or 5th toes
- Palpable intermetatarsal mass or tenderness
- Absence of joint instability (negative drawer test) - would suggest synovitis instead
Common Pitfalls
- Don't dismiss the tingling: This symptom differentiates nerve pathology from pure joint disease
- Don't assume all forefoot pain is "metatarsalgia": This is a descriptive term, not a diagnosis 2
- Location matters: Pain "over" the MTP joint can originate from the intermetatarsal space below
- If drawer test is positive and joint instability is present, reconsider toward MTP synovitis/instability as primary diagnosis
Next Steps for Confirmation
- MRI if diagnosis uncertain - will show neuroma and rule out synovitis
- Ultrasound can identify interdigital neuromas
- Diagnostic injection of local anesthetic into the intermetatarsal space (therapeutic and diagnostic)
The presence of tingling is the critical clinical clue that elevates Morton's neuroma above other MTP pathologies in the differential diagnosis hierarchy.