Key distinguishing features of the most common diagnoses
|Very Tender Joint(s)||Yes||No||Possible||No||No|
|Pain at Rest||Yes||No||No||Possible||No|
Possible:Urinalysis, FBC, ESR/CRP, rheumatoid factor/anti-CCP antibodies, uric acid, X-ray.
Small Print:Bone scan, angiography.
- Urinalysis may reveal glycosuria in previously undiagnosed diabetic with neuropathy (suspicion of neuropathy may in itself require further investigations).
- FBC/ESR/CRP: Raised WCC and ESR/CRP in infection and severe inflammation.
- Rheumatoid factor: Of prognostic help if foot pain is part of clinical diagnosis of rheumatoid arthritis (consider anti-CCP antibodies if negative).
- Uric acid: If gout suspected, especially with recurrent attacks and if considering prophylaxis.
- X-ray useful if suspect possible arthritis, osteomyelitis, march fracture, osteochondritis, radio-opaque foreign body. If clinical suspicion high and X-ray unhelpful, bone scan may be more useful.
- Angiography: If ischaemic foot with rest pain.
- The vast majority of causes are obvious from the history or from a cursory examination. The harder you have to think, the more likely that there may be an obscure cause requiring investigation.
- It can be difficult to distinguish gout from a severely inflamed bunion. With gout, the patient may have had previous episodes, the onset tends to be sudden, the joint is extremely tender and joint movements are very limited.
- Important pointers can be picked up in the history, especially for some of the less common causes. Thus, Morton’s neuroma causes a sharp pain often radiating to the third and fourth toes, relieved by removing the shoe; plantar fasciitis is described as ‘walking on a pebble’, especially after resting; and a march fracture results in a pain which initially comes on predictably with exercise and which then becomes continuous, with local bony tenderness and possibly a lump.
- If a known arteriopath complains of pain in the ball of the foot disturbing sleep then the diagnosis is probably critical ischaemia. Refer urgently.
- Fever and systemic illness with localised extreme bone pain and signs of local infection is acute osteomyelitis or septic arthritis until proved otherwise. Admit.
- Pain with no obvious signs – particularly tenderness – in the foot suggests ischaemia, neuropathy or an L5/S1 nerve root lesion.
- If no cause is evident but the patient has very localised sole tenderness away from the heel, consider a foreign body.