Investigations for Elderly Patients with Mononeuritis Multiplex
Begin with nerve conduction studies and electromyography to confirm the diagnosis and characterize the pattern of nerve involvement, followed by targeted laboratory testing for vasculitis and systemic inflammatory conditions, which are the most common treatable causes in this population. 1
Essential Electrodiagnostic Studies
- Nerve conduction studies (NCS) and electromyography are mandatory to confirm mononeuritis multiplex and differentiate it from polyneuropathy or other peripheral nerve disorders 1
- These studies identify the specific nerves involved and establish the asymmetric pattern characteristic of mononeuritis multiplex 1
Core Laboratory Investigations
Vasculitis Screening (Highest Priority)
- ANCA testing (both MPO and PR3) is essential when vasculitis is suspected, as ANCA-associated vasculitis is a leading cause of mononeuritis multiplex 1
- Complete blood count with differential to detect eosinophilia, which suggests eosinophilic granulomatosis with polyangiitis (EGPA) 1, 2
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to assess systemic inflammation 1
Autoimmune and Rheumatologic Panel
- Antinuclear antibody (ANA) and extractable nuclear antigens, as systemic lupus erythematosus accounts for approximately 36% of rheumatic disease-associated cases 3
- Rheumatoid factor and anti-CCP antibodies for rheumatoid vasculitis 1
- Complement levels (C3, C4) to evaluate for complement-mediated vasculitis 1
- Anti-Ro/SSA and anti-La/SSB antibodies for Sjögren's syndrome, which can cause mononeuritis multiplex 1
Metabolic and Infectious Workup
- Comprehensive metabolic panel to assess renal function, as vasculitis often involves kidneys 1
- Hemoglobin A1c to exclude diabetes mellitus, though this is typically evident from history 3
- Hepatitis B and C serologies, as these can cause cryoglobulinemic vasculitis 1
- HIV testing, as HIV-associated vasculitis can present with mononeuritis multiplex 1
Additional Investigations Based on Clinical Context
When Vasculitis is Strongly Suspected
- Deep skin biopsy reaching medium-sized vessels is recommended when polyarteritis nodosa is suspected, as superficial biopsies may miss the diagnosis 1
- Sural nerve biopsy can confirm vasculitis histologically, though it was non-diagnostic in some reported cases 4
When Inflammatory Demyelinating Process is Considered
- CSF analysis is recommended when inflammatory demyelinating polyradiculoneuropathy enters the differential, looking for albuminocytologic dissociation 1
Malignancy Screening in Elderly Patients
- Age-appropriate cancer screening is important, as lymphoma and other malignancies can present with mononeuritis multiplex 3
- Serum protein electrophoresis and immunofixation to exclude paraproteinemic neuropathy 5
- Lactate dehydrogenase as a marker of lymphoproliferative disorders 6
Critical Pitfalls to Avoid
- Do not rely solely on history and physical examination to exclude rheumatic disease: In one study, 0% of patients without clinical suspicion of rheumatic disease had one identified on laboratory testing, but this represents a confidence interval of 0-18%, meaning occult disease cannot be completely excluded 3
- Do not delay treatment while awaiting biopsy results in severe cases: Early initiation of therapy is associated with better neurological outcomes, as delay leads to severe irreversible deficits 1
- Do not assume a negative initial workup excludes vasculitis: Some patients require repeat testing or tissue diagnosis, particularly when clinical suspicion remains high 1, 7
- Be aware that approximately 54% of mononeuritis multiplex cases remain idiopathic even after comprehensive evaluation, so negative workup does not preclude the diagnosis 3