Mononeuritis multiplex as clinical presentation of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneously presenting, chronic, multisystem autoimmune disease. Neurological manifestations of SLE can affect both central and peripheral nervous systems and are associated with reduced health-related quality of life and increased mortality.1-3 While most neurological manifestations occur around the time of SLE diagnosis, they may precede diagnosis, creating diagnostic and therapeutic challenges. Mononeuritis multiplex (MNM) is a rare SLE manifestation, usually occuring years after diagnosis.4 We present an 11-year-old girl who presented with severe, rapidly progressive MNM due to SLE. This is the first report of MNM as the initial SLE manifestation in a pediatric patient, and only the second report of MNM at time of SLE diagnosis.5 This previously healthy 11-year-old girl presented with progressively worsening distal right leg pain, antalgic gait, and intermittent fever, preceded by recent influenza A infection. Her evaluation was significant for normocytic anemia, elevated inflammatory markers, and magnetic resonance imaging (MRI) suggestive of an inflammatory myopathy (Figure 1). The differential diagnosis included postinfectious reactive myositis versus new-onset chronic immune-mediated inflammatory disease. She was discharged on a prednisone taper with further evaluation pending. Over the next month, her examination became progressively more abnormal, with increasingly severe distal upper and lower extremity weakness, pain, paresthesias, muscle atrophy, and gait instability. She developed bilateral claw hand deformity and foot drop, absent toe flexion and extension, and absent Achilles reflexes. Brain MRI demonstrated abnormal small T2 hyperintensity in the right lateral pons. Spine MRI and lumbar puncture were normal. Figure 1 shows bilateral lower extremity MRI, with abnormalities interpreted as myositis versus neurogenic atrophy. Nerve conduction and electromyography demonstrated severe axonal sensory and motor neuropathy with asymmetric involvement, consistent with mononeuritis multiplex. The presence of this neuropathy and patchy myopathic changes supported clinical diagnosis of vasculitic neuropathy. Muscle biopsy of left vastus lateralis demonstrated neurogenic atrophy without perivascular or endomysial inflammation (Figure 2). However, as the biopsy was completed after an initial steroid course, potential inflammatory muscular findings may have been masked. With a likely diagnosis of rapidly progressive MNM from vasculitic neuropathy, extensive multidisciplinary diagnostic evaluation for potential etiologies continued. Prior rheumatologic evaluation had been pertinent for positive antinuclear antibody, and despite any specific clinical manifestations for SLE outside of neurological disease, a full evaluation revealed high-titer positive SS-A antibody (>8.0 ai), positive dsDNA antibody, RNP antibody, and low positive cardiolipin IgM antibody. A diagnosis of SLE-associated MNM was made and treatment was initiated with high-dose corticosteroids, monthly IV cyclophosphamide, and hydroxychloroquine. Six months after treatment initiation, the girl showed significant improvements in motor function, pain, and sensation. She ambulated independently with normal strength in proximal lower limb muscles. However, she had continued hand small muscle weakness, loss of pain and vibration sensation in distal extremities, and bilateral foot drop and weak plantarflexion. Repeat nerve conduction and electromyography showed improvement, with reinnervation in previously denervated muscles. She had no additional clinical or laboratory evidence of active SLE. Our patient presented with acute right lower extremity pain rapidly progressing to MNM affecting all extremities. MRI showed hyperintense signal on STIR and T2 imaging sequences with contrast enhancement, initially interpreted as myositis. However, further studies including electromyography, nerve conduction, and muscle biopsy were consistent with axonal injuries to nerves, and diagnosis of SLE-related MNM was made after extensive evaluation. MNM is a rare manifestation of SLE usually accompanied by multisystem disease. A broad differential must be evaluated in patients presenting with unusual neuropathic symptomatology. Early recognition and aggressive treatment are critical in minimizing morbidity and mortality due to MNM.6 Our patient illustrates the difficulty in recognizing isolated MNM due to unsuspected SLE and the potential functional response to immunotherapy. Natalie Weston: Conceptualization; project administration; visualization; writing—original draft; writing—review and editing. Audrey Cortesi: Writing—original draft; writing—review and editing. Vettaikorumakankav Vedanarayanan: Writing—original draft; writing—review and editing. Jamie Shanahan: Writing—original draft; writing—review and editing. Rosemary G. Peterson: Conceptualization; project administration; supervision; visualization; writing—original draft; writing—review and editing. The authors declare no conflicts of interest.