Pearls & Oy-sters: Bilateral Mononeuropathic Neuralgic Amyotrophy Triggered by Bartonella henselae Infection Responsive to Immunoglobulin

Pearls

• Bartonella henselae infection is a rare cause of bilateral neuralgic amyotrophy.

Oy-sters

• Patients with neuralgic amyotrophy, especially when bilateral, need a comprehensive workup to exclude rare infectious causes such as hepatitis E and, in case of suggestive history, Bartonella henselae infection.

• An intravenous immunoglobulin treatment trial may be considered, even in cases with poor clinical prognosis.

Case Report

A 50-year-old cat owner with an unremarkable medical history recognized a small scratch injury on his right thenar region, without noticing a cat scratch or an insect bite. After 3 days, his thenar eminence became swollen, tender, and painful with expanding redness around the wound. He incised the wound with secretion of purulent liquid. After another 2–3 days, he developed febrile temperatures and noticed swollen but painless lymph nodes in the right axilla. Inflammatory markers were slightly elevated (CRP 18.5 mg/L, normal <5 mg/L; leucocytes 14.7 G/L, normal range 3.0–10.5 G/L; with normal differential count). An oral therapy with amoxicillin-clavulanic acid 3 × 625 mg/d was prescribed empirically by his general practitioner. Two days later, he noticed electric sensations radiating anteriorly from his right elbow to his lower arm and hand for several hours, followed by pain in his hand and paresthesia in his volar thumb and index finger. Within the next 2 days, he noted numbness in his distal thumb and index fingers bilaterally with evolving inability to flex the distal interphalangeal joints. Furthermore, he noticed patchy numbness over his right ventral thigh. The general practitioner took blood cultures and a serology for B. henselae. Blood cultures were negative, but IgG titers (by indirect fluorescence assay) were highly elevated (>1:1,024), and IgM was negative. Antibiotic therapy was changed to azithromycin 500 mg/d on the first day, followed by 250 mg/d for 4 further days. After one week with persistent neurologic deficits, Bartonella serology was repeated showing even higher IgG titers of >1:4,096, and IgM was again negative. Twelve days after starting antibiotic treatment (9 days after starting azithromycin), a lumbar puncture was performed with normal cell count (4 mononuclear cells/ul) and normal values for protein (316 mg/L, normal 150–450 mg/L), glucose, and lactate. However, 2 CSF-specific oligoclonal bands were detected without signs of blood–brain barrier disturbance. A CSF culture remained negative and Bartonella polymerase chain reaction (PCR). Lymph node biopsy revealed an expansion of the interfollicular zone with isolated B plasma cells without signs of lymphoma, granulomas, or Bartonella detected by PCR. Serology tests for Toxoplasma gondii, Treponema pallidum, Borrelia burgdorferi, HIV, and hepatitis B, C, and E viruses were negative. No vasculitic antibodies or ganglioside antibodies were detected in the serum.

One month after onset, the patient was referred to our center for neuromuscular diseases. On examination, the patient was unable to feel light touch, temperature, and pinprick in the volar right distal thumb and index finger and the left distal thumb. The patient had a Medical Research Council's scale (MRC) muscle strength grade M0 for flexion of the distal interphalangeal joints of both thumbs (Figure 1). Flexion of the distal index finger was M0 on the right side and M4 on the left side. The muscle strength for supination of the right hand was M4. On the right thigh, he indicated decreased sensation for light touch in a patchy distribution, not corresponding to a specific nerve. Deep tendon reflexes were brisk and symmetric in all extremities.

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Figure 1 Clinical Presentation

The patient was asked to make a fist (A) and to flex the proximal and distal interphalangeal joints of his thumb (B) The patient was unable to flex both distal interphalangeal joints of digit I and II (MRC grad 0).

Motor nerve conduction study (NCS) of the median nerve with recording from the abductor pollicis brevis muscle showed slightly prolonged distal motor latency (right 4.4 ms, left 5.2 ms; normal <4.0 ms) with normal amplitudes and normal conduction velocity of proximal segments on both sides. Sensory NCS of the median nerve was unremarkable. Motor and sensory NCS of the ulnar nerve on both sides were normal. Needle myography of the right flexor pollicis longus muscle and pronator quadratus muscle showed a prolonged insertional activity and moderate fibrillation potentials and positive sharp waves without the detection of volitional motor activity. Needle myography of the right abductor pollicis brevis muscle and interosseous dorsalis I muscle were unremarkable.

At 6 months after disease onset, a MR neurography (3 T, Magnetom SkyraFit, Siemens, Erlangen, Germany; spine and body coils used) of the right brachial plexus and arm nerves were performed using high-resolution T2-weighted, fat-suppressed sequences. The examination revealed irregular hyperintense signal abnormalities and short segments of enlarged nerve fascicle bundles of the right median nerve in the middle and distal upper arm, corresponding somatotopically to nerve fascicle bundles of the anterior interosseous nerve and proximal muscular branches of the median nerve (Figure 2). Signs of muscle denervation (diffuse hyperintense signal abnormalities) were found in the pronator teres, flexor carpi radialis, and flexor digitorum profundus muscles. The nerve structure and signal intensity of the plexus brachialis and the distal segments of the median nerve below the elbow were normal; all other arm nerves were without pathologic imaging findings.

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Figure 2. MRI High-Resolution T2-Weighted, Fat-Suppressed Sequences of the Right Brachial Plexus and Arm Nerves

(A) Irregular hyperintense signal abnormalities and short segments of enlarged nerve fascicle bundles of the right median nerve in the right proximal upper arm (red arrow) and (B) normal-appearing median nerve (red arrow) in the right lower arm with signs of muscle denervation (diffuse hyperintense signal abnormalities) in the right pronator teres muscle (a), flexor carpi radialis muscle (b), and flexor digitorum profundus muscle (c).

A treatment trial of oral prednisolone (1 mg/kg body weight per day for 1 month) one month after symptom onset was unsuccessful. Another treatment trial with intravenous immunoglobulin (IVIG; 0.4 mg/kg body weight over 5 days every 4 weeks) was started 10 months after onset because of difficulty in obtaining reimbursement of IVIG treatment cost for off-label use. The patient showed a significant clinical response within the first 2 weeks after treatment, resulting in only mild residual weakness of finger flexion of distal interphalangeal joints of thumbs (right M4, left M5) and index fingers (right M5-, left M5), without any residual sensory disturbance. After another 5 cycles of IVIG, the patient achieved an almost complete recovery, showing only a minimal deficit in the flexion of the right distal thumb. The electrophysiologic follow-up assessment revealed a normalization of the motor NCS of the median nerve bilaterally. Therefore, we are now starting a tentative treatment pause.