Nerve Involvement and Deformities in Leprosy
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Direct answer
Nerve involvement in leprosy is the main cause of disability, because Mycobacterium leprae invades peripheral nerves and damages their sensory, motor and autonomic fibres. Untreated nerve damage produces claw hand, foot drop, lagophthalmos and trophic ulcers. WHO disability grading, from grade 0 to grade 2, records sensory loss and visible damage in the eyes, hands and feet, and it guides both care and follow-up.
What you must remember
- Commonest nerves: ulnar, median, common peroneal, posterior tibial, facial and greater auricular nerves.
- Claw hand: ulnar nerve damage, with clawing of the ring and little fingers and wasting of the intrinsic hand muscles.
- Ape hand: median nerve damage, with thumb wasting and loss of thumb opposition.
- Foot drop: common peroneal nerve damage, with inability to dorsiflex the ankle.
- Lagophthalmos: facial nerve damage that prevents full eyelid closure and exposes the cornea.
- Trophic ulcers: anaesthetic hands and feet injured by repeated pressure or trauma.
- WHO grade 1: loss of sensation in the eyes, hands or feet without visible deformity.
- WHO grade 2: visible deformity or damage, such as claw hand, foot drop or lagophthalmos.
A stepwise nerve examination
A patient with a thickened ulnar nerve and a clawed ring finger has nerve damage, not only a deformity. Early detection, before the nerve is destroyed, is the main aim of the examination, so each nerve is checked in turn.
- Palpate the nerves: Feel the ulnar, median, common peroneal, posterior tibial and greater auricular nerves for thickening and tenderness.
- Test sensation: Use light touch, pinprick and a monofilament over the hands and feet, since numbness is often patchy at first.
- Test muscle power: Check the small hand muscles and the wrist and ankle movements, and note any wasting, which signals motor loss.
- Examine the eyes: Test eyelid closure and corneal sensation, because facial nerve and trigeminal involvement can cause silent corneal damage.
- Grade the disability: Score the eyes, hands and feet using the WHO grades, recording any visible deformity or ulcer as grade 2.
- Start early treatment: Treat with multidrug therapy and use systemic steroids for acute neuritis, since nerve function can recover if the damage is caught early.
- Protect and rehabilitate: Provide footwear, hand protection, splints and eye care, with physiotherapy or surgery for established deformities.
Where the exam tries to catch you
Most traps involve mixing up nerve patterns or assuming that deformity is reversible.
- Trap: attributing claw hand to median nerve damage Correct: claw hand of the ring and little fingers is ulnar nerve damage, whereas ape hand suggests median nerve injury.
- Trap: expecting foot drop from posterior tibial involvement Correct: foot drop comes from the common peroneal nerve, while posterior tibial damage causes plantar anaesthesia.
- Trap: ignoring lagophthalmos as a cosmetic issue Correct: incomplete eye closure risks corneal exposure and blindness, so it needs eye protection and early review.
- Trap: treating established deformity as reversible with drugs alone Correct: once a deformity is fixed, multidrug therapy cannot undo it, and splinting or surgery is needed.
Frequently asked questions
Which nerves are most commonly involved in leprosy?
The commonest nerves involved in leprosy are the ulnar, median, common peroneal, posterior tibial, facial and greater auricular nerves. The ulnar and common peroneal nerves are most often linked to visible deformity.
What is the difference between claw hand and ape hand in leprosy?
Claw hand in leprosy results from ulnar nerve damage, causing clawing of the ring and little fingers. Ape hand results from median nerve damage, with wasting of the thumb muscles and loss of thumb opposition.
What does WHO disability grading record in leprosy?
WHO disability grading records the extent of disability in the eyes, hands and feet. Grade 0 means no impairment, grade 1 means sensory loss without visible deformity, and grade 2 means visible deformity or damage such as lagophthalmos.
Why is lagophthalmos dangerous in leprosy?
Lagophthalmos is incomplete eye closure caused by facial nerve damage, and it exposes the cornea. Untreated corneal exposure can lead to ulceration and blindness, so patients with lagophthalmos need eye protection and regular review.
Is nerve damage in leprosy reversible?
Nerve damage in leprosy can improve when it is treated early, especially with steroids for acute neuritis alongside multidrug therapy. Established deformities such as claw hand or foot drop are often permanent and need splinting, physiotherapy or surgery.