Editors' Note: Clinical Reasoning: A 65-Year-Old Woman With Cancer History and Wrist Drop
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Although the neurologic examination has its imperfections, the key to etiologic assessment and diagnostic testing of focal neurologic deficits lies in lesion localization. Merrill et al. narrate a stepwise approach to localization and diagnostic testing for their patient with wrist drop and arm numbness. Dr. Zhai emphasizes that lesions which spare the triceps and brachioradialis muscles suggest a lesion in the distal part of the radial nerve (posterior interosseous branch). Thus, they wondered why the triceps muscle was spared in this patient with an axillary mass. The authors note that the lymphomatous mass was extensive in their patient and extended from the radial nerve to the lateral cord of the brachial plexus and involved some arm muscles directly. Although lateral cord involvement was noted (which gives rise to the musculocutaneous and median nerves), there were no symptoms or signs associated with that observation. Furthermore, there seems to be sparing of the posterior cord of the plexus which supplies the triceps muscle. The authors indicate that electromyography and nerve conduction studies aided in localization by confirming a lack of a radial sensory response and abnormal radial motor responses with reduced recruitment in the brachioradialis (without involvement of the triceps)—supporting a localization of the injury to the radial nerve at, or distal to, the spiral groove. Furthermore, the extensive perineural invasion of the lymphoma involved both the radial nerve and the lateral cord during gross resection. Although PET imaging and regions of tumor resection suggested involvement of the brachial plexus, the microscopic involvement of lymphoma is likely beyond the spatial resolution of present-day imaging. This exchange highlights the complementary nature of the examination, electrodiagnostic studies, and neuroimaging. Sometimes all the tests do not perfectly line up, and clinical summation takes precedence.
Although the neurologic examination has its imperfections, the key to etiologic assessment and diagnostic testing of focal neurologic deficits lies in lesion localization. Merrill et al. narrate a stepwise approach to localization and diagnostic testing for their patient with wrist drop and arm numbness. Dr. Zhai emphasizes that lesions which spare the triceps and brachioradialis muscles suggest a lesion in the distal part of the radial nerve (posterior interosseous branch). Thus, they wondered why the triceps muscle was spared in this patient with an axillary mass. The authors note that the lymphomatous mass was extensive in their patient and extended from the radial nerve to the lateral cord of the brachial plexus and involved some arm muscles directly. Although lateral cord involvement was noted (which gives rise to the musculocutaneous and median nerves), there were no symptoms or signs associated with that observation. Furthermore, there seems to be sparing of the posterior cord of the plexus which supplies the triceps muscle. The authors indicate that electromyography and nerve conduction studies aided in localization by confirming a lack of a radial sensory response and abnormal radial motor responses with reduced recruitment in the brachioradialis (without involvement of the triceps)—supporting a localization of the injury to the radial nerve at, or distal to, the spiral groove. Furthermore, the extensive perineural invasion of the lymphoma involved both the radial nerve and the lateral cord during gross resection. Although PET imaging and regions of tumor resection suggested involvement of the brachial plexus, the microscopic involvement of lymphoma is likely beyond the spatial resolution of present-day imaging. This exchange highlights the complementary nature of the examination, electrodiagnostic studies, and neuroimaging. Sometimes all the tests do not perfectly line up, and clinical summation takes precedence.
Footnotes
Author disclosures are available upon request (journal{at}neurology.org).
- Received November 21, 2022.
- Accepted in final form November 21, 2022.
- © 2023 American Academy of Neurology
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