Isolated finger flexion: a novel form of focal neuromyotonia

Abstract

Two almost identical elderly women are described who presented with gradually progressive painless involuntary flexion of the ring and middle fingers over 12 months, leading eventually to contractures. The flexion deformity persisted during sleep and was the sole neurological abnormality. Both patients had advanced chronic obstructive pulmonary disease and were on long term salbutamol and oxygen. Neurophysiological studies indicated that this was due to neuromyotonia mainly involving flexor digitorum superficialis muscles without evidence of underlying peripheral neuropathy, proximal conduction block, or generalised neuromyotonia. Voltage gated potassium channel antibodies were negative. The clinical and neurophysiological picture remained static over a 2 year follow up period. It is suggested that this is a novel form of acquired focal neuromyotonia and speculate both on its cause and distribution. We describe an apparently novel clinical phenomenon characterised by flexion deformity of the middle and ring fingers due to isolated focal neuromyotonia in two elderly patients. Case 1A 78 year old woman presented with a 12 month history of gradually worsening painless involuntary flexion of the left middle and ring fingers associated with some tightness of the left forearm and occasional paraesthesia in the fingertips. Her symptoms increased until her fingers were fully and forcefully flexed against her palm. She also developed similar but milder symptoms in the right hand. Most manual functions apart from pinch grip were impaired. The abnormal finger posture persisted during sleep.She had severe chronic obstructive pulmonary disease (COPD) and was taking regular nebulised salbutamol (up to 5 mg four times daily), oxygen, and prednisolone.Examination showed continuous involuntary flexion of the middle and ring fingers at the metacarpophalangeal and the proximal inter-

Teaching Video NeuroImage: Clenched Fists as an Unusual Presentation of Focal Neuromyotonia

“…Whereas the pathomechanisms remain elusive, enhanced axonal hyperexcitability secondary to COPD-induced hypoxemia as well as hyperpolarization from sympathomimetics, through their effects on voltage-gated Na+/K+ pumps, may result in ectopic firing in high-frequency bursts. 1,2 Other cases have also been found in association with a more generalized voltage-gated potassium channel antibody autoimmunity, 3 although these antibodies were absent in the current case.…”

“…The current case illustrates an unusual but treatable presentation of the rare focal form of neuromyotonia, 1,2 and should be differentiated from other conditions that may have similar presentations such as myotonic dystrophy and other nondystrophic myotonias, ulnar neuropathies, and Dupuytren contracture, the latter of which may result in unnecessary surgical intervention. As with the current case, patients previously reported with this condition tend to be older women with a history of chronic obstructive pulmonary disease (COPD) managed by inhaled β2 sympathomimetics.…”

Teaching Video NeuroImage: Clenched Fists as an Unusual Presentation of Focal Neuromyotonia

“…Whereas the pathomechanisms remain elusive, enhanced axonal hyperexcitability secondary to COPD-induced hypoxemia as well as hyperpolarization from sympathomimetics, through their effects on voltage-gated Na+/K+ pumps, may result in ectopic firing in high-frequency bursts. 1,2 Other cases have also been found in association with a more generalized voltage-gated potassium channel antibody autoimmunity, 3 although these antibodies were absent in the current case.…”

“…The current case illustrates an unusual but treatable presentation of the rare focal form of neuromyotonia, 1,2 and should be differentiated from other conditions that may have similar presentations such as myotonic dystrophy and other nondystrophic myotonias, ulnar neuropathies, and Dupuytren contracture, the latter of which may result in unnecessary surgical intervention. As with the current case, patients previously reported with this condition tend to be older women with a history of chronic obstructive pulmonary disease (COPD) managed by inhaled β2 sympathomimetics.…”

Segmental neuromyotonia

“…This focal involvement is either in the form of involvement of digits of extremities or extraocular muscles [ Table 1 ]. [ 2 3 4 5 6 7 8 9 ]…”

Focal neuromyotonia associated with a C9ORF72 expansion mutation

“…4 Moreover, we ruled out other causes of focal neuromyotonia, as this peculiar clinic-EMG syndrome was described in multifocal motor neuropathy, chronic radiculopathies, and, more rarely, with compression neuropathies. 1 Obviously, it is possible that the C9ORF72 repeat expansion may act as a risk factor rather than a causal factor in our…”

Teaching Video NeuroImage: Clenched Fists as an Unusual Presentation of Focal Neuromyotonia

“…Whereas the pathomechanisms remain elusive, enhanced axonal hyperexcitability secondary to COPD-induced hypoxemia as well as hyperpolarization from sympathomimetics, through their effects on voltage-gated Na+/K+ pumps, may result in ectopic firing in high-frequency bursts. 1,2 Other cases have also been found in association with a more generalized voltage-gated potassium channel antibody autoimmunity, 3 although these antibodies were absent in the current case.…”

“…The current case illustrates an unusual but treatable presentation of the rare focal form of neuromyotonia, 1,2 and should be differentiated from other conditions that may have similar presentations such as myotonic dystrophy and other nondystrophic myotonias, ulnar neuropathies, and Dupuytren contracture, the latter of which may result in unnecessary surgical intervention. As with the current case, patients previously reported with this condition tend to be older women with a history of chronic obstructive pulmonary disease (COPD) managed by inhaled β2 sympathomimetics.…”

Segmental neuromyotonia

“…This focal involvement is either in the form of involvement of digits of extremities or extraocular muscles [ Table 1 ]. [ 2 3 4 5 6 7 8 9 ]…”

Focal neuromyotonia associated with a C9ORF72 expansion mutation

“…4 Moreover, we ruled out other causes of focal neuromyotonia, as this peculiar clinic-EMG syndrome was described in multifocal motor neuropathy, chronic radiculopathies, and, more rarely, with compression neuropathies. 1 Obviously, it is possible that the C9ORF72 repeat expansion may act as a risk factor rather than a causal factor in our…”

Teaching Video NeuroImage: Clenched Fists as an Unusual Presentation of Focal Neuromyotonia

“…Whereas the pathomechanisms remain elusive, enhanced axonal hyperexcitability secondary to COPD-induced hypoxemia as well as hyperpolarization from sympathomimetics, through their effects on voltage-gated Na+/K+ pumps, may result in ectopic firing in high-frequency bursts. 1,2 Other cases have also been found in association with a more generalized voltage-gated potassium channel antibody autoimmunity, 3 although these antibodies were absent in the current case.…”

“…The current case illustrates an unusual but treatable presentation of the rare focal form of neuromyotonia, 1,2 and should be differentiated from other conditions that may have similar presentations such as myotonic dystrophy and other nondystrophic myotonias, ulnar neuropathies, and Dupuytren contracture, the latter of which may result in unnecessary surgical intervention. As with the current case, patients previously reported with this condition tend to be older women with a history of chronic obstructive pulmonary disease (COPD) managed by inhaled β2 sympathomimetics.…”

Segmental neuromyotonia

“…This focal involvement is either in the form of involvement of digits of extremities or extraocular muscles [ Table 1 ]. [ 2 3 4 5 6 7 8 9 ]…”

Focal neuromyotonia associated with a C9ORF72 expansion mutation

“…4 Moreover, we ruled out other causes of focal neuromyotonia, as this peculiar clinic-EMG syndrome was described in multifocal motor neuropathy, chronic radiculopathies, and, more rarely, with compression neuropathies. 1 Obviously, it is possible that the C9ORF72 repeat expansion may act as a risk factor rather than a causal factor in our…”