What's in a name?: Lumping or splitting ALS, PLS, PMA, and the other motor neuron diseases

Motor phenotypes of amyotrophic lateral sclerosis - a three-determinant anatomical classification based on the region of onset, propagation of motor symptoms, and the degree of upper and lower motor neuron dysfunction

BACKGROUND

In amyotrophic lateral sclerosis (ALS), heterogeneity of motor phenotypes is a fundamental hallmark of the disease. Distinct ALS phenotypes were associated with a different progression and survival. Despite its relevance for clinical practice and research, there is no broader consensus on the classification of ALS phenotypes.

METHODS

An expert consensus process for the classification of ALS motor phenotypes was performed from May 2023 to December 2024. A three-determinant anatomical classification was proposed which is based on the (1) region of onset (O), (2) the propagation of motor symptoms (P), and (3) the degree of upper (UMN) and/or lower motor neuron (LMN) dysfunction (M). Accordingly, this classification is referred to as the "OPM classification".

RESULTS

Onset phenotypes differentiate the site of first motor symptoms: O1) head onset; O2d) distal arm onset; O2p) proximal arm onset; O3r) trunk respiratory onset; O3a) trunk axial onset; O4d) distal leg onset; O4p) proximal leg onset. Propagation phenotypes differentiate the temporal propagation of motor symptoms from the site of onset to another, vertically distant body region: PE) earlier propagation (within 12 months of symptom onset); PL) later propagation (without propagation within 12 months of symptom onset), including the established phenotypes of "progressive bulbar paralysis" (O1, PL), "flail-arm syndrome" (O2p, PL), and "flail-leg syndrome" (O4d, PL); PN) propagation not yet classifiable as time since symptom onset is less than 12 months. Phenotypes of motor neuron dysfunction differentiate the degree of UMN and/or LMN dysfunction: M0) balanced UMN and LMN dysfunction; M1d) dominant UMN dysfunction; M1p) pure UMN dysfunction ("primary lateral sclerosis", PLS); M2d) dominant LMN dysfunction; M2p) pure LMN dysfunction ("progressive muscle atrophy", PMA); M3) dissociated motor neuron dysfunction with dominant LMN and UMN dysfunction of the arms and legs ("brachial amyotrophic spastic paraparesis"), respectively.

CONCLUSION

This consensus process aimed to standardize the clinical description of ALS motor phenotypes in clinical practice and research - based on the onset region, propagation pattern, and motor neuron dysfunction. This "OPM classification" contributes to specifying the prognosis, to defining the inclusion or stratification criteria in clinical trials and to correlate phenotypes with the underlying disease mechanisms of ALS.

Unraveling the complex interplay between genes, environment, and climate in ALS

Various genetic and environmental risk factors have been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). Despite this, the cause of most ALS cases remains obscure. In this review, we describe the current evidence implicating genetic and environmental factors in motor neuron degeneration. While the risk exerted by many environmental factors may appear small, their effect could be magnified by the presence of a genetic predisposition. We postulate that gene-environment interactions account for at least a portion of the unknown etiology in ALS. Climate underlies multiple environmental factors, some of which have been implied in ALS etiology, and the impact of global temperature increase on the gene-environment interactions should be carefully monitored. We describe the main concepts underlying such interactions. Although a lack of large cohorts with detailed genetic and environmental information hampers the search for gene-environment interactions, newer algorithms and machine learning approaches offer an opportunity to break this stalemate. Understanding how genetic and environmental factors interact to cause ALS may ultimately pave the way towards precision medicine becoming an integral part of ALS care.

Neuropsychological Functioning in PLS: A Comparison with ALS

Objective:

In order to characterize the nature and extent of neuropsychological dysfunction in primary lateral sclerosis (PLS), we studied prospectively cognitive, emotional, and behavioral functioning in PLS, and compared performances to functioning in amyotrophic lateral sclerosis (ALS).

Methods:

Eighteen patients with PLS and 13 patients with ALS completed a neuropsychological test battery assessing both cognitive skills and emotional/behavioral functioning.

Results:

Both PLS and ALS groups scored broadly within normal limits (mean T-scores greater than 40) on all cognitive measures and no significant between-group differences were found with the exception of one variable. However, when examined on a case by case basis, the data revealed considerable heterogeneity amongst patients in both groups. Overall, 39% of PLS patients and 31% of ALS patients were considered cognitively impaired. A higher than expected frequency of abnormal scores was noted for several tests of executive function in both groups, and a majority of PLS patients also exhibited abnormal behavioural symptoms. There was no relationship in PLS or ALS groups between cognitive functioning and disease duration, current site of disease, site of onset, functional status, and respiratory variables. Comparison between the PLS and ALS groups indicated virtually no differences in cognitive test scores and overall emotional/behavioural symptoms.

Conclusions:

We observed deficits in cognition and behaviour in a significant proportion of PLS patients which were comparable to those observed in ALS cases. Although deficits were not in the range of frontotemporal dementia, both ALS and PLS cases demonstrated deficits most prominently on tests of executive functioning.

Challenges in the Understanding and Treatment of Amyotrophic Lateral Sclerosis/Motor Neuron Disease

With the acceleration in our understanding of ALS and the related motor neuron disease has come even greater challenges in reconciling all of the proposed pathogenic mechanisms and how this will translate into impactful treatments. Fundamental issues such as diagnostic definition(s) of the disease spectrum, relevant biomarkers, the impact of multiple novel genetic mutations and the significant effect of symptomatic treatments on disease progression are all areas of active investigation. In this review, we will focus on these key issues and highlight the challenges that confront both clinicians and basic science researchers.

Peripheral nerve ultrasound in amyotrophic lateral sclerosis phenotypes

INTRODUCTION

In this study we sought to determine the cross-sectional area (CSA) of peripheral nerves in patients with distinct subtypes of amyotrophic lateral sclerosis (ALS).

METHODS

Ulnar and median nerve ultrasound was performed in 78 ALS patients [classic, n = 21; upper motor neuron dominant (UMND), n = 14; lower motor neuron dominant (LMND), n = 20; bulbar, n = 15; primary lateral sclerosis (PLS), n = 8] and 18 matched healthy controls.

RESULTS

Compared with controls, ALS patients had significant, distally pronounced reductions of ulnar CSA (forearm/wrist level) across all disease groups, except for PLS. Median nerve CSA (forearm/wrist level) did not differ between controls and ALS.

CONCLUSION

Ulnar nerve ultrasound in ALS subgroups revealed significant differences in distal CSA values, which suggests it has value as a marker of LMN involvement. Its potential was particularly evident in the UMND and PLS groups, which can be hard to separate clinically, yet their accurate separation has major prognostic implications.

Quantifying disease progression in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) exhibits characteristic variability of onset and rate of disease progression, with inherent clinical heterogeneity making disease quantitation difficult. Recent advances in understanding pathogenic mechanisms linked to the development of ALS impose an increasing need to develop strategies to predict and more objectively measure disease progression. This review explores phenotypic and genetic determinants of disease progression in ALS, and examines established and evolving biomarkers that may contribute to robust measurement in longitudinal clinical studies. With targeted neuroprotective strategies on the horizon, developing efficiencies in clinical trial design may facilitate timely entry of novel treatments into the clinic.

Predicting the severity of motor neuron disease progression using electronic health record data with a cloud computing Big Data approach

Motor neuron diseases (MNDs) are a class of progressive neurological diseases that damage the motor neurons. An accurate diagnosis is important for the treatment of patients with MNDs because there is no standard cure for the MNDs. However, the rates of false positive and false negative diagnoses are still very high in this class of diseases. In the case of Amyotrophic Lateral Sclerosis (ALS), current estimates indicate 10% of diagnoses are false-positives, while 44% appear to be false negatives. In this study, we developed a new methodology to profile specific medical information from patient medical records for predicting the progression of motor neuron diseases. We implemented a system using Hbase and the Random forest classifier of Apache Mahout to profile medical records provided by the Pooled Resource Open-Access ALS Clinical Trials Database (PRO-ACT) site, and we achieved 66% accuracy in the prediction of ALS progress.

Latent cluster analysis of ALS phenotypes identifies prognostically differing groups

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a degenerative disease predominantly affecting motor neurons and manifesting as several different phenotypes. Whether these phenotypes correspond to different underlying disease processes is unknown. We used latent cluster analysis to identify groupings of clinical variables in an objective and unbiased way to improve phenotyping for clinical and research purposes.

METHODS

Latent class cluster analysis was applied to a large database consisting of 1467 records of people with ALS, using discrete variables which can be readily determined at the first clinic appointment. The model was tested for clinical relevance by survival analysis of the phenotypic groupings using the Kaplan-Meier method.

RESULTS

The best model generated five distinct phenotypic classes that strongly predicted survival (p<0.0001). Eight variables were used for the latent class analysis, but a good estimate of the classification could be obtained using just two variables: site of first symptoms (bulbar or limb) and time from symptom onset to diagnosis (p<0.00001).

CONCLUSION

The five phenotypic classes identified using latent cluster analysis can predict prognosis. They could be used to stratify patients recruited into clinical trials and generating more homogeneous disease groups for genetic, proteomic and risk factor research.

Clinical phenotypes and natural progression for motor neuron disease: analysis from an Australian database

From 1997 to 2003 we prospectively followed a cohort of ALS/MND patients. Patients were allocated to predetermined clinical phenotypes using the principles established in the modified El Escorial criteria. The date and region of symptom onset were carefully determined and their progression was scored using the Appel ALS rating scale. The four distinct clinical phenotypes: Global, Flail Arm, Flail Leg and Primary Lateral Sclerosis (PLS) demonstrated significantly different rates of progression and survival times. The Global ALS/MND phenotype can present with initial symptoms in any region and rapidly progresses to involve all segments, with symptoms due to a mixture of combined corticospinal tract and anterior horn cell dysfunction. The Global phenotype has the shortest survival and most rapid rate of disease progression. There was a significant difference in survival between Global bulbar onset and cervical onset disease but no significant difference in the rate of disease progression between the three Global subgroups as determined by the Appel/ALS rating scale. Flail patients had much slower rates of progression and significantly longer survival compared to the Global phenotype. Patients with Primary Lateral Sclerosis as expected progressed the slowest and survived the longest compared to the other clinical phenotypes. The utility of developing a method of assigning clinical phenotypes with similar survival and disease progression rates is discussed in relation to therapeutic trial design, practice benchmarking and clinico-pathological correlations.

Upper motor neuron and extra-motor neuron involvement in amyotrophic lateral sclerosis: a clinical and brain imaging review

There is an ongoing discussion whether ALS is primarily a disease of upper motor neurons or lower motor neurons. We undertook a review to assess how new insights have contributed to solve this controversy. For this purpose we selected relevant publications from 1995 onwards focussing on (1) primary targets and disease progression in ALS and variants of ALS, (2) brain imaging markers for upper motor neuron lesion, and (3) evidence for ALS being a multisystem disorder. Clinically, upper motor and lower motor neuron symptoms can occur in any order over time. Brain imaging markers show upper motor neuron involvement in early disease. Overlap syndromes of ALS and dementia, and involvement of autonomic and sensory nerves occur frequently. PET/SPECT scans, functional MRI and voxel based morphometry studies clearly show abnormalities in extra-motor areas of the brain. Pathologically, the 43 kDa TAR DNA-binding protein (TDP-43) provides a clue to these overlapping disorders. In conclusion, evidence accumulates that ALS is a multisystem disorder rather than a pure lower and/or upper motor neuron disorder.

[Primary lateral sclerosis: the era of international diagnosis criteria]

Since Charcot's first description, primary lateral sclerosis (PLS) remains a rare clinical syndrome, a neuropathological phenotype of motor system degeneration. In turn, PLS has been described as belonging to the large spectrum of motoneuron diseases or to the diverse degenerative diseases of the nervous system. Clinically, it is characterized by progressive pyramidal involvement in patients who present insidiously progressive gait disorders and, on examination, have relatively symmetrical lower limb weakness, increased muscle tone, pathologic hyper-reflexia, and exaggerated extensor plantar responses. Pinprick, light touch, and temperature sensations are preserved. Viewed in another way, PLS mimicks progressive hereditary spastic paraparesis (HSP) and the "central" phenotype of amyotrophic lateral sclerosis (ALS). PLS is considered "idiopathic" and, depending on the presence or absence of similarly affected family members, the syndrome of idiopathic HSP and ALS are labeled "hereditary" or "apparently sporadic". The juvenile form of PLS and early age at onset in cases of HSP complicate our understanding of the relationship between these two disorders. Guidelines for diagnosis and genetic counseling have been published for HSP and ALS. Recently, since the first international workshop, guidelines for diagnosis of PLS propose a classification system, e.g. for heterogeneous HSP into "pure PLS", complicated or "plus PLS", symptomatic PLS and upper motor neuron-dominant ALS. However, when reviewing known cases of PLS drawn from the literature, rigorous retrospective application of these new PLS criteria raises an unanswered question: does pure PLS exist?

Levetiracetam: part II, the clinical profile of a novel anticonvulsant drug

The objective of this article was to review and summarize the available reports on the profile of the novel anticonvulsant drug levetiracetam (LEV) in a clinical setting. Therefore, a careful search was conducted in the MEDLINE database and combined with guidelines from regulatory agencies, proceedings of professional scientific meetings, and information provided by the manufacturers. This article is devoted to the clinical pharmacology and clinical trials of LEV investigating its efficacy and safety as add-on therapy or monotherapy for various seizure types. Finally, results from postmarketing surveillance of LEV are briefly discussed. In general, LEV is shown to be a safe, broad-spectrum anticonvulsant drug with highly beneficial pharmacokinetic properties, a favorable long-term retention rate, and a high responder rate, indicating that LEV is an efficient therapeutic option for the treatment of several types of epilepsy.

Monomelic neurogenic syndromes: a prospective study

Monomelic neurogenic syndromes are rare. Their classification and prognostic features have not been addressed in the European population. A prospective study of 17 patients with monomelic neurogenic amyotrophy, of upper or lower limb onset, with progression limited to one limb for three or more years. Clinical and neurophysiological studies were performed in the subsequent 3 or more years. Fifteen patients were of European origin and two were Asian. Those presenting with proximal monomelic weakness or with involvement of the posterior compartment of the lower leg showed no further progression after the initial period of development of the syndrome. Brisk reflexes in wasted muscles did not predict progression. Electromyographic signs of denervation in the opposite limb at presentation did not predict later progression. Transcranial magnetic stimulation (TMS) features of corticospinal dysfunction were a useful predictor of subsequent progression (p=0.01). One patient with lower limb onset developed conduction block with weakness in an upper limb nine years after presentation, and this upper limb weakness responded to IVIg therapy. This adult-onset European group of patients is different as compared with juvenile-onset Asian cases. The clinical syndromes appear heterogeneous, but neurophysiological investigations, in particular TMS, can be helpful in determining prognosis. Multifocal motor neuropathy should be considered when there is progression, even years after onset.

Classification of Phenotype Characteristics in Adult-Onset Spinal Muscular Atrophy

BACKGROUND/AIMS

Degenerative lower motor neuron diseases (LMND) encompass a group of rare clinically and genetically heterogeneous disorders with the hallmark of anterior horn cell degeneration in the spinal cord and brainstem. In a recently proposed classification, LMND were subdivided according to the clinical disease pattern and time course. This study was performed to investigate the clinical practicability of the classification.

METHODS

In 22 patients with adult LMND (mean disease duration, 24 years), the disease course and detailed clinical, electrophysiological, magnetic resonance imaging, laboratory, and genetic investigations were analyzed.

RESULTS

All patients could be assigned to the distinct disease subgroups, i.e. 11 patients to the slowly progressive generalized form (group 1), one to the distal form (group 2), 3 to the segmental distal form (group 3a), and seven to the segmental proximal form (group 3b).

CONCLUSIONS

The proposed classification was confirmed to be a practicable tool, and additional implications for the classification of LMND could be drawn from the data in our patient sample.