The Split Hand Syndrome in Amyotrophic Lateral Sclerosis
The Split Hand Syndrome in Amyotrophic Lateral Sclerosis
Wilbourn stressed that not every ALS patient with hand wasting showed the split hand phenomenon and sometimes muscle wasting could be more or less equal between the lateral and medial hand muscles, especially when the disease was advanced. Very rarely were the hypothenar muscles more severely affected than the muscles of the lateral hand (reversed split hand). Furthermore, the split hand was not completely specific to ALS, and Wilbourn encountered it in several other conditions, including Werdnig–Hoffmann disease, 'benign' focal motor neuron disease and remote poliomyelitis. However, "the demonstration of a split hand during nerve conduction studies on a patient referred to the EMG laboratory with suspected ALS was considered to be a very ominous finding and subsequent needle electrode examination almost never demonstrated any alternative diagnosis".
The split hand has been rarely reported in patients with non-ALS related 'pure lower motor neuron disease'—namely, autosomal dominant distal spinal muscular atrophy, spinocerebellar ataxia type 3 (Machado–Joseph disease) and juvenile muscular atrophy, as well as spinal and bulbar muscular atrophy (SBMA). There are only a few causes of painless hand wasting in the absence of sensory deficit, as is typical of ALS. These include thenar wasting from a cervical rib and band, spondylotic cord compression, compression of the deep motor branch of the ulnar nerve and carpal tunnel syndrome in the elderly, in whom there may be moderate or marked thenar wasting with little if any sensory deficit, and a C8 root lesion. All of these conditions have characteristic clinical and electrophysiological features, and the split hand phenomenon has not been reported in any of these conditions (see figure 1).
A multicentre Japanese study systematically examined the sensitivity and specificity of the split hand in ALS (The Tokyo Metropolitan Neuromuscular Electrodiagnosis Study group). There were 77 patients with ALS, 171 normal subjects and 199 patients with other disorders affecting lower motor neurons/axons, such as spinal muscular atrophy, SBMA and axonal polyneuropathies. The split hand was strictly defined as APB/ADM CMAP amplitude ratio <0.6 or FDI/ADM ratio <0.9 (mean−3SD of the normal control data). Based on the electrophysiological criteria, split hand was found in 52% of ALS patients, in 5% of normal subjects and in 13% of disease controls. Among the disease controls, two patients with SBMA showed split hand; in ALS patients, the split is found with moderate sensitivity (52%) and high specificity (95% vs normal controls and 87% vs disease controls). A recent study has described the use of a novel neurophysiological measure of the split hand, 'the split hand index'. This is the ratio of the CMAP amplitude of the APB times the CMAP amplitude of the FDI divided by the CMAP amplitude of the ADM. This study needs confirmation but appears to be a robust measure of split hand in ALS.
Sensitivity, Specificity and Diagnostic Utility
Wilbourn stressed that not every ALS patient with hand wasting showed the split hand phenomenon and sometimes muscle wasting could be more or less equal between the lateral and medial hand muscles, especially when the disease was advanced. Very rarely were the hypothenar muscles more severely affected than the muscles of the lateral hand (reversed split hand). Furthermore, the split hand was not completely specific to ALS, and Wilbourn encountered it in several other conditions, including Werdnig–Hoffmann disease, 'benign' focal motor neuron disease and remote poliomyelitis. However, "the demonstration of a split hand during nerve conduction studies on a patient referred to the EMG laboratory with suspected ALS was considered to be a very ominous finding and subsequent needle electrode examination almost never demonstrated any alternative diagnosis".
The split hand has been rarely reported in patients with non-ALS related 'pure lower motor neuron disease'—namely, autosomal dominant distal spinal muscular atrophy, spinocerebellar ataxia type 3 (Machado–Joseph disease) and juvenile muscular atrophy, as well as spinal and bulbar muscular atrophy (SBMA). There are only a few causes of painless hand wasting in the absence of sensory deficit, as is typical of ALS. These include thenar wasting from a cervical rib and band, spondylotic cord compression, compression of the deep motor branch of the ulnar nerve and carpal tunnel syndrome in the elderly, in whom there may be moderate or marked thenar wasting with little if any sensory deficit, and a C8 root lesion. All of these conditions have characteristic clinical and electrophysiological features, and the split hand phenomenon has not been reported in any of these conditions (see figure 1).
A multicentre Japanese study systematically examined the sensitivity and specificity of the split hand in ALS (The Tokyo Metropolitan Neuromuscular Electrodiagnosis Study group). There were 77 patients with ALS, 171 normal subjects and 199 patients with other disorders affecting lower motor neurons/axons, such as spinal muscular atrophy, SBMA and axonal polyneuropathies. The split hand was strictly defined as APB/ADM CMAP amplitude ratio <0.6 or FDI/ADM ratio <0.9 (mean−3SD of the normal control data). Based on the electrophysiological criteria, split hand was found in 52% of ALS patients, in 5% of normal subjects and in 13% of disease controls. Among the disease controls, two patients with SBMA showed split hand; in ALS patients, the split is found with moderate sensitivity (52%) and high specificity (95% vs normal controls and 87% vs disease controls). A recent study has described the use of a novel neurophysiological measure of the split hand, 'the split hand index'. This is the ratio of the CMAP amplitude of the APB times the CMAP amplitude of the FDI divided by the CMAP amplitude of the ADM. This study needs confirmation but appears to be a robust measure of split hand in ALS.
