The split hand syndrome in amyotrophic lateral sclerosis
Bibliographic record
Abstract
In amyotrophic lateral sclerosis (ALS), hand muscle wasting preferentially affects the 'thenar (lateral) hand', including the abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles, with relative sparing of the hypothenar muscles (the abductor digiti minimi (ADM)). This peculiar pattern of dissociated atrophy of the intrinsic hand muscles is termed the 'split hand' and is rarely seen in diseases other than ALS. The muscles involved in the split hand are innervated through the same spinal segments (C8 and T1), and FDI and ADM, which are differentially affected, are both ulnar nerve innervated. The physiological mechanisms underlying the split hand in ALS are incompletely understood but both cortical and spinal/peripheral mechanisms are probably involved. Motor potentials evoked by magnetic stimulation are significantly smaller when recorded from the thenar complex, compared with the hypothenar muscles, supporting a cortical mechanism. But peripheral axonal excitability studies have suggested that APB/FDI motor axons have more prominent persistent sodium currents than ADM axons, leading to higher axonal excitability and thereby more ready degeneration. Pincer or precision grip is vital to human hand function, and frequent use of thenar complex muscles may lead to greater oxidative stress and metabolic demands at both upper and lower motoneurons innervating the APB and FDI. The split hand is a useful diagnostic sign in early ALS, and recent objective studies indicate that the sign has a high degree of specificity.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".