Vasculitic Neuropathy and Mononeuritis Multiplex
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Direct answer
Vasculitic neuropathy is nerve injury caused by inflammation of the small vessels supplying peripheral nerves, and it most often presents as mononeuritis multiplex, an asymmetric pattern of separate nerve involvement. Systemic vasculitis, leprosy, cryoglobulinaemia and hepatitis C are important causes to consider. A sural nerve biopsy may confirm the diagnosis, and treatment targets the cause, with immunosuppression for severe systemic disease.
What you must remember
- Pattern: mononeuritis multiplex, with asymmetric, multifocal involvement of individual nerves that often develops in steps or suddenly.
- Systemic vasculitis: polyarteritis nodosa, ANCA-associated vasculitis such as granulomatosis with polyangiitis and microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis, often with skin, renal or lung involvement.
- Infective causes: leprosy, hepatitis B and C, and HIV, with hepatitis C linked to cryoglobulinaemic vasculitis.
- Leprosy: a major cause of mononeuritis multiplex in India, with thickened, tender ulnar, median, common peroneal and posterior tibial nerves.
- Electrophysiology: nerve conduction studies show an axonal, asymmetric and multifocal pattern in affected nerves, rather than a symmetric length-dependent picture.
- Biopsy: a sural nerve biopsy may show necrotising vasculitis of epineurial vessels, and it is the most useful confirmatory test in suspected cases.
- Blood tests: ESR and CRP, ANCA, ANA, complement levels, cryoglobulins, hepatitis B and C serology and HIV testing are sent together.
- Treatment: corticosteroids with cyclophosphamide or rituximab for severe systemic vasculitis, antiviral therapy for hepatitis C, and multidrug therapy for leprosy.
Narrowing the cause of multiple nerve palsies
Mononeuritis multiplex is a pattern rather than a diagnosis, so the cause is narrowed by matching the systemic clues with a specific test. The table links the likely causes to what they look like and how they are confirmed.
| Cause | Systemic clue | Specific test |
|---|---|---|
| Systemic vasculitis | Fever, weight loss, renal or lung involvement | ANCA, biopsy of an affected organ or nerve |
| Leprosy | Hypopigmented skin patches, thickened nerves | Slit skin smear and nerve examination |
| Hepatitis C cryoglobulinaemia | Purpura, arthralgia, renal disease | Serum cryoglobulins and hepatitis C RNA |
| Diabetic mononeuropathy | Known diabetes, cranial or truncal nerves | Blood glucose and HbA1c |
Leprosy and diabetes are common alternatives in Indian practice, so they are excluded before a vasculitis is labelled. The biopsy should sample a clinically affected nerve, with the sural nerve chosen because it is accessible and often involved.
Worked example: a 50-year-old man develops a right wrist drop over days, followed by a left foot drop, with fever and weight loss. ANCA is positive, and a sural nerve biopsy shows necrotising vasculitis of epineurial vessels, so the diagnosis is systemic vasculitic neuropathy.
Where the examiner tests the pattern
Questions typically describe a patient with sequential nerve palsies and ask for the cause or the next test.
- Trap: Attributing asymmetric deficits in several nerves to simple entrapment. Correct: Involvement of separate nerves points to mononeuritis multiplex, a vasculitic or infective process rather than a single compression.
- Trap: Starting immunosuppression without excluding leprosy or hepatitis C. Correct: These infections must be excluded first, because they need specific treatment and immunosuppression can worsen viral infections.
- Trap: Treating active vasculitis with physiotherapy alone. Correct: Physiotherapy and splinting are supportive, while active systemic vasculitis needs immunosuppression.
Frequently asked questions
What is mononeuritis multiplex?
Mononeuritis multiplex is the involvement of two or more separate peripheral nerves, typically in an asymmetric and multifocal pattern. It often develops in steps or suddenly, with pain and sensory or motor loss in each nerve's territory. Vasculitis, infection and cryoglobulinaemia are the main causes to consider.
Which investigation confirms vasculitic neuropathy?
Sural nerve biopsy is the most useful confirmatory test for vasculitic neuropathy in suspected cases, and it can show necrotising vasculitis of epineurial vessels. Nerve conduction studies show multifocal axonal changes, while ANCA and other systemic markers suggest the underlying disease. The biopsy result is interpreted alongside the clinical picture.
Why must leprosy be excluded in mononeuritis multiplex?
Leprosy must be excluded because it is a major cause of mononeuritis multiplex in India and needs multidrug therapy rather than immunosuppression. Thickened nerves, hypopigmented skin patches with sensory loss and, in multibacillary disease, a positive slit skin smear help make the diagnosis. Reversal reactions, which damage nerves further, are managed with steroids under specialist care.
How does diabetic mononeuropathy differ from vasculitic neuropathy?
Diabetic mononeuropathy typically affects cranial or truncal nerves in a patient with known diabetes, whereas vasculitic neuropathy involves limb nerves with systemic features. Diabetic mononeuropathy often recovers over weeks to months as glucose control improves. Serum ANCA and inflammatory markers help separate the two conditions.