diagnosis
Patients present with the classical clinical picture of dorsiflexion and eversion of the foot, and of extension of the toes, resulting in a foot drop and a characteristic slapping gait (1).
Obtaining a thorough medical history is important:
- inquire about the possibility of external pressure of the nerve
- habitual leg crossing, habitual or prolonged squatting or kneeling (may be work related)
- confinement to bed
- use of leg brace or recent plaster cast below the knee
- use of leg positioning or leg supports during recent surgery
- other causes of compression at the fibular neck
- check for any precipitating factor
- recent weight loss (“slimmer’s palsy”)
- overstretched peroneal nerve (owing to ankle strain or prolonged leg stretching)
- masses in the popliteal space (for example, Baker’s cysts)
- identify other causes of neuropathy or mononeuritis multiplex from medical history e.g. - diabetes, alcohol misuse, vitamin B12 deficiency, or chemotherapy
- exclude acute trauma or surgery causing direct injury to the nerve
- inquire about other weakness or sensory problems of the leg(s), lower back, or arms
- painless foot drop without any associated neurological symptoms is almost always due to peroneal monomeuropathy
- painful footdrop may be caused by L5 radiculopathy, trauma, lumbar plexopathy, or mononeuritis multiplex
Physical examination of the patient:
- examine
- patient’s gait
- severe weakness of the dorsiflexion muscles may cause a high stepping gait (to avoid dragging of the foot)
- observe while the patient is walking on the heels and toes and if there is difficulty walking on the heel, peripheral neuropathy is the likely cause
- patient’s legs
- signs of trauma like swelling or erythema which may suggest compartment syndrome
- fasciculations in legs and arms –may be due to a more extensive neurological problem (such as motor neurone disease)
- for reduced pain (pin prick) sensation and light touch in the (lower) legs and feet
- deep peroneal nerve lesions will cause sensory abnormalities only in the first web space while abnormalities in the anterolateral aspect of the lower leg and the foot dorsum may indicate a superficial peroneal nerve lesion
- classic textbook description of sensory loss is usually not seen except in total nerve laceration
- generally sensory loss is restricted to the dorsum of the foot and some toes while in some patients sensory symptoms or signs are absent
- assess strength of
- foot dorsiflexion and eversion - peroneal nerve
- foot plantar flexion and inversion - tibial nerve
- hip abduction - superior gluteal nerve, L5 nerve root
- check for signs indicating upper motor neurone disease
- knee and Achilles’ tendon reflexes for hyper-reflexia and plantar response for Babinski’s sign
- assess for local tenderness along the course of the common peroneal nerve and for pressure neuropathy by eliciting Tinel’s sign (1,2)
Patients with isolated peroneal mononeuropathy will
- present with weakness of foot dorsiflexion or eversion (or both).
- normal reflexes and absent leg pain, swelling, or erythema (2)
Electromyography or nerve conduction studies may be considered to confirm the diagnosis after careful examination of the patient (1,2)
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