- Case report
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A case report of isolated distal upper extremity weakness due to cerebral metastasis involving the hand knob area
© The Author(s). 2018
- Received: 20 February 2018
- Accepted: 26 September 2018
- Published: 3 October 2018
Unilateral weakness of an upper extremity is most frequently caused by traumatic nerve injury or compression neuropathy. In rare cases, lesion of the central nervous system may result in syndromes suggesting peripheral nerve damage by the initial examination. Pseudoperipheral hand palsy is the best known of these, most frequently caused by a small lesion in the contralateral motor cortex of the brain. The ‘hand knob’ area refers to a circumscribed region in the precentral gyrus of the posterior frontal lobe, the lesion of which leads to isolated weakness of the upper extremity mimicking peripheral nerve damage. The etiology of this rare syndrome is almost exclusively related to an embolic infarction.
We present the case of a 70-year-old male patient with isolated left sided upper extremity weakness and clumsiness without sensory disturbance suggesting a lesion of the radial nerve. Nerve conduction studies had normal results excluding peripheral nerve damage. Neuroimaging (cranial CT and MRI) detected 3 space occupying lesions, one of them in the right precentral gyrus. An irregularly shaped tumor was found by CT in the left lung with multiple associated lymph node conglomerates. The metastasis from this mucinous tubular adenocarcinoma with solid anaplastic parts to the ‘hand knob’ area was responsible for the first clinical sign related to the pulmonary malignancy.
Pseudoperipheral palsy of the upper extremity is not necessarily the consequence of an embolic stroke. If nerve conduction studies have normal results, neuroimaging – preferably MRI – should be performed, as lesion in the hand-knob area of the precentral gyrus can also be caused by a malignancy.
- Isolated distal upper extremity weakness
- Hand knob
- Brain metastasis
Isolated upper extremity weakness is predominantly attributed to an injury of the peripheral nervous system. Weakness resulting from damage of the radial, ulnar, or median nerve are most commonly due to traumatic injury or compression neuropathy; however, it may develop as a symptom in association with other conditions including amyotrophic lateral sclerosis, cervical radiculopathy, or thoracic outlet syndrome. Isolated weakness of the upper extremity is rare in central nervous system damage. In such cases lesions of the motor cortex or of the downstream corticospinal tract are responsible for the clinical signs. The ‘hand knob’ area is a circumscribed region of the motor cortex in the precentral gyrus of the posterior frontal lobe , the lesion of which leads to isolated weakness of the contralateral upper extremity mimicking peripheral nerve damage. This rare symptom is almost exclusively related to an underlying cortical infarction. The lesion presents in a misleading symptomatology, raising the suspicion of peripheral neuropathy, which may pose a challenge in the differential diagnosis.
Isolated upper extremity weakness is rarely caused by a lesion localized to the central nervous system. As the clinical signs suggest peripheral neuronal disease, the usual workup of such patients starts with nerve conduction studies. With normal results of the electrophysiological tests, another etiology should be searched. An injury to a circumscribed territory of the precentral gyrus (primary motor cortex) referred to as ‘hand knob’ results in clinical signs mimicking peripheral nerve lesion that is called “pseudoperipheral” palsy. According to the Penfield-Rasmussen map, primary motor neurons innervating the upper extremity are localized in the lower third of the dorsolateral surface of the precentral gyrus [1, 7]. This region of the precentral gyrus is a knob-like structure, reminiscent of an epsilon or an omega in the axial functional MRI scans, whereas resembling a hook in the sagittal scans . The etiology behind this rare symptom is almost exclusively reported to be a cortical infarction [3, 9–14], with hardly any reference to alternative causes . Intraoperative cortical stimulation, functional MRI and navigated transcranial magnetic stimulation studies clearly identified the region in the precentral gyrus of the posterior frontal lobe which is associated with hand movements, therefore should be saved during neurosurgical interventions, like resections of primary and metastatic brain tumors in the perirolandic area [6, 16, 17].
Our case confirms that circumscribed damage to the hand knob resulting in isolated distal upper extremity weakness may be caused not only by cerebral ischemia but also by a brain metastasis. The isolated weakness of the upper extremity was the first and only symptom that initiated the diagnostic process, eventually leading to the diagnosis of a primary pulmonary malignancy. The clinical diagnosis was confirmed by autopsy and histopathological examination.
Although it has been suggested that patients with isolated hand palsy without alternative explanations for peripheral damage should be aggressively treated for acute ischemic stroke , pseudoperipheral palsy of the upper extremity is not necessarily the consequence of an ischemic cerebrovascular lesion. If nerve conduction studies have normal results, neuroimaging should be performed, as a lesion in the hand-knob area of the precentral gyrus can also be caused by a malignancy affecting this region. As CT misses the hand knob lesion in a considerable rate, MRI should be the preferred neuroimaging method.
DB was supported by the Higher Education Institutional Excellence Program of the Ministry of Human Resources of the Government of Hungary.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Availability of data and materials
The original material (confidential patient record) is available at Szent Janos Hospital, Department of Neurology, Budapest, Hungary.
AF: patient examination, clinical management, medical record preparation, clinical neurological supervision, first draft of manuscript, concept, approval of final manuscript. VV: patient examination, clinical management, approval of final manuscript. GV: MRI neuroimaging, interpretation of results, manuscript preparation, critical review and approval of final manuscript. LK: MRI neuroimaging, critical review and approval of final manuscript. MB: CT neuroimaging, critical review and approval of final manuscript. ES: electrophysiological examination, interpretation of electrophysiological results, critical review and approval of final manuscript. KAB-M: neurological management, manuscript preparation, approval of final manuscript. ZK: pulmonological supervision of the case, critical review and approval of final manuscript. DB: concept, critical review of initial versions of the manuscript, preparation of the final version of the manuscript.
Ethics approval and consent to participate
This case presentation did not involve any specific intervention therefore no ethics approval was needed. Data were collected retrospectively for this manuscript after the death of the patient. As only the usual diagnostic practice was followed, no specific consent was needed from the patient. The usual consent requested from patients for routine hospital care is documented in the patient’s medical records.
Consent for publication
The outcome unfortunately was fatal, therefore the written consent to publish was given by a relative. The signed consent form is available on request.
The authors declare that they have no competing interests.
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