Chapter 20 Lower limb pain

Case 20.1

1. What is your differential diagnosis for:

a the lesions over the metatarsal heads

Plantar warts, seborrheic keratoses, actinic keratoses, arsenical keratoses, squamous cell carcinoma.

b the dark coloured lesions

Plantar warts, seborrheic keratoses, actinic keratoses, arsenical keratoses, squamous cell carcinoma, malignant melanoma.

2. What do you recommend to your patient?

To have them assessed by a medical practitioner, in order to eliminate serious pathology.

3. What is the most likely diagnosis?

Plantar warts.

4. What is the aetiology of these lesions?

Human papilloma virus.

5. Why have some of the lesions darkened?

Plantar warts can develop thrombi within their capillaries, which can give them a darker colour.

6. Why are they more commonly associated with pain, compared to their more ‘common’ relatives?

This is due to the depth to which they grow.

Case 20.2

1. What is your differential diagnosis?

Possible diagnoses are:

• erythema nodosum

• erysipelas

• nodular vasculitis

• familial Mediterranean fever.

2. From the appearance shown in Figure 20.2, what are the two most likely?

The two most likely are:

i erythema nodosum

ii erysipelas.

3. State the likely aetiology for each of these disorders.

i Erythema nodosum: infective agents (streptococcus is the most common); some drugs (eg: sulphonamides, sulphonylureas, oral contraceptive pill, gold); chronic inflammatory bowel diseases; lymphomas; sarcoidosis, Bechet disease and pregnancy.^[1]

ii Erysipelas: streptococci causes the majority of cases.

Case 20.3

1. What are the possible causes of her pain?

Causes could possibly be caused by:

• compartment syndrome

• fracture site not fully stabilised, causing further damage

• excessive swelling with a cast applied too tightly

• deep vein thrombosis

• embolus.

2. For each of these causes, describe the most likely pathogenesis for her pain.

Possible cause	Pathogenesis of pain
Compartment syndrome	Pain is due to ischaemia to tissue resulting from a decrease in perfusion pressure at the fracture site. This may be due to a range of factors, including significant oedema or a haemorrhage
Fracture site not fully stabilised, causing further damage	If the fracture site has not been fully immobilised, there may be displacement of bony fragments, causing stimulation of nociceptors or pressure on nerves
Excessive swelling with a cast applied too tightly	Excess fluid in a myofascial compartment may cause pain. May be a precursor to compartment syndrome
Deep vein thrombosis	May occur due to stasis of blood flow as a result of immobilisation
Embolus	Unlikely, but needs to be considered. Pain occurs due to anoxia of tissues and a build up of lactic acid and other metabolites

3. How can you determine which of these causes are responsible?

This patient must be referred immediately for an urgent workup. Refer to Wallace, Goodman and Smith for details.^[2]

Case 20.4

1. What is your differential diagnosis?

Possible diagnoses are:

• iliotibial pain syndrome

• ligamentous damage

• tendon strain.

2. What physical examination tests can you do in order to narrow your differential diagnosis?

• Palpate knee for swelling and tenderness.

• Test muscle strength.

• Ober test—to determine tightness in the iliotibial tract.

• Modified Thomas test—to assess flexibility of hip flexors, hamstrings and iliotibial tract.

3. What is the most likely diagnosis?

Iliotibial pain syndrome.

4. Who is most susceptible to this condition?

The most susceptible people are:

• long distance runners

• cyclists

• tennis players.

5. What is the most likely pathogenesis in Ben’s situation?

This is possibly due to incorrect positioning on his bicycle. Any imbalance between muscle groups may exacerbate the condition.

Case 20.5

1. What is your differential diagnosis based only on the history?

Possible diagnoses are:

• metatarsalgia

• Morton’s neuroma

• stress fracture

• tarsal tunnel syndrome.

2. How does this information help you with narrowing your differential diagnosis? Which is the most likely diagnosis?

• The most likely diagnosis is metatarsalgia.

• Tarsal tunnel syndrome is less likely with normal sensation. However, this condition may occur without neurological deficit.

• Morton’s neuroma is not likely due to:

the lack of a discrete swelling

lack of tenderness between metatarsal heads

a negative metatarsal squeeze test.

3. What are some of the predisposing factors and causes of the most likely diagnosis you named in question 2?

There are a number of factors which predispose an individual to this disorder. Please refer to Durham for detail.^[3]

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