Progressive muscular atrophy
|Progressive muscular atrophy|
|Other names||Duchenne–Aran muscular atrophy, others|
Progressive muscular atrophy (PMA) is a very rare subtype of motor neuron disease (MND) that affects only the lower motor neurons. PMA is thought to account for around 4% of all MND cases. This is in contrast to amyotrophic lateral sclerosis (ALS), the most common form of MND, which affects both the upper and lower motor neurons, or primary lateral sclerosis, another rare MND variant, which affects only the upper motor neurons. The distinction is important because PMA is associated with a better prognosis than classic ALS.
Signs and symptoms
As a result of lower motor neuron degeneration, the symptoms of PMA include:
Some patients have symptoms restricted only to the arms or legs (or in some cases just one of either). These cases are referred to as flail limb either flail arm or flail leg, and are associated with a better prognosis.
PMA is a diagnosis of exclusion, there is no specific test which can conclusively establish whether a patient has the condition. Instead, a number of other possibilities have to be ruled out, such as multifocal motor neuropathy or spinal muscular atrophy. Tests used in the diagnostic process include MRI, clinical examination, and EMG. EMG tests in patients who do have PMA usually show denervation (neuron death) in most affected body parts, and in some unaffected parts too.
It typically takes longer to be diagnosed with PMA than ALS, an average of 20 months for PMA vs 15 months in ALS/MND.
- brisk reflexes
- Babinski's sign
- emotional lability
The importance of correctly recognizing progressive muscular atrophy as opposed to ALS is important for several reasons.
- 1) the prognosis is a little better. A recent study found the 5-year survival rate in PMA to be 33% (vs 20% in ALS) and the 10-year survival rate to be 12% (vs 6% in ALS).
- 2) Patients with PMA do not suffer from the cognitive change identified in certain groups of patients with MND.
- 3) Because PMA patients do not have UMN signs, they usually do not meet the "World Federation of Neurology El Escorial Research Criteria" for “Definite” or “Probable” ALS and so are ineligible to participate in the majority of clinical research trials such as drugs trials or brain scans.
- 4) Because of its rarity (even compared to ALS) and confusion about the condition, some insurance policies or local healthcare policies may not recognize PMA as being the life-changing illness that it is. In cases where being classified as being PMA rather than ALS is likely to restrict access to services, it may be preferable to be diagnosed as "slowly progressive ALS" or "lower motor neuron predominant" ALS.
An initial diagnosis of PMA could turn out to be slowly progressive ALS many years later, sometimes even decades after the initial diagnosis. The occurrence of upper motor neuron symptoms such as brisk reflexes, spasticity, or a Babinski sign would indicate a progression to ALS; the correct diagnosis is also occasionally made on autopsy.
Despite being rarer than ALS, PMA was described earlier, when in 1850 French neurologist François Aran described 11 cases which he termed atrophie musculaire progressive. Contemporary neurologist Guillaume-Benjamin-Amand Duchenne de Boulogne English: // also claimed to have described the condition 1 year earlier, although the written report was never found. The condition has been called progressive muscular atrophy (PMA), spinal muscular atrophy (SMA), Aran–Duchenne disease, Duchenne–Aran disease, Aran–Duchenne muscular atrophy, and Duchenne–Aran muscular atrophy. The name "spinal muscular atrophy" is ambiguous as it refers to any of various spinal muscular atrophies, including the autosomal recessive spinal muscular atrophy caused by a genetic defect in the SMN1 gene.
Disease or syndrome
Since its initial description in 1850, there has been debate in the scientific literature over whether PMA is a distinct disease with its own characteristics, or if lies somewhere on a spectrum with ALS, PLS, and PBP. Jean-Martin Charcot, who first described ALS in 1870, felt that PMA was a separate condition, with degeneration of the lower motor neurons the most important lesion, whereas in ALS it was the upper motor neuron degeneration that was primary, with lower motor neuron degeneration being secondary. Such views still exist in archaic terms for PMA such as "Primary progressive spinal muscular atrophy". Throughout the course of the late 19th century, other conditions were discovered which had previously been thought to be PMA, such as pseudo-hypertrophic paralysis, hereditary muscular atrophy, progressive myopathy, progressive muscular dystrophy, peripheral neuritis, and syringomyelia.
The neurologists Joseph Jules Dejerine and William Richard Gowers were among those who felt that PMA was part of a spectrum of motor neuron disease which included ALS, PMA, and PBP, in part because it was almost impossible to distinguish the conditions at autopsy. Other researchers have suggested that PMA is just ALS in an earlier stage of progression, because although the upper motor neurons appear unaffected on clinical examination there are in fact detectable pathological signs of upper motor neuron damage on autopsy.
Also, no gene has been linked specifically to PMA, and the disorder does not appear in the OMIM database.
In favour of considering PMA a separate disease, some patients with PMA live for decades after diagnosis, which would be unusual in typical ALS.
To this day, terminology around these diseases remains confusing because in the United Kingdom motor neurone disease refers to both ALS specifically and to the spectrum of ALS, PMA, PLS, and PBP. In the United States the most common terms are ALS (both specifically for ALS and as a blanket term) or Lou Gehrig's disease.
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- Wijesekera LC, Mathers S, Talman P, Galtrey C, Parkinson MH, Ganesalingam J, Willey E, Ampong MA, Ellis CM, Shaw CE, Al-Chalabi A, Leigh PN (Mar 2009). "Natural history and clinical features of the flail arm and flail leg ALS variants". Neurology. 72 (12): 1087–1094. doi:10.1212/01.wnl.0000345041.83406.a2. PMC 2821838. PMID 19307543.
- Visser J, de Visser M, Van den Berg-Vos RM, Van den Berg LH, Wokke JH, de Jong JM, Franssen H (May 2008). "Interpretation of electrodiagnostic findings in sporadic progressive muscular atrophy". J. Neurol. 255 (6): 903–909. doi:10.1007/s00415-008-0813-y. PMID 18484238.
- Wicks P, Abrahams S, Leigh PN, Williams T, Goldstein LH (Nov 2006). "Absence of cognitive, behavioral, or emotional dysfunction in progressive muscular atrophy". Neurology. 67 (9): 1718–1719. doi:10.1212/01.wnl.0000242726.36625.f3. PMID 17101922.
- Tsuchiya K, Sano M, Shiotsu H, Akiyama H, Watabiki S, Taki K, Kondo H, Nakano I, Ikeda K (Sep 2004). "Sporadic amyotrophic lateral sclerosis of long duration mimicking spinal progressive muscular atrophy exists: additional autopsy case with a clinical course of 19 years". Neuropathology. 24 (3): 228–235. doi:10.1111/j.1440-1789.2004.00546.x. PMID 15484701.
- Ince PG, Evans J, Knopp M, Forster G, Hamdalla HH, Wharton SB, Shaw PJ (Apr 2003). "Corticospinal tract degeneration in the progressive muscular atrophy variant of ALS". Neurology. 60 (8): 1252–1258. doi:10.1212/01.wnl.0000058901.75728.4e. PMID 12707426.
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Progressive muscular atrophy
Title: Internal medicine; a work for the practicing physician on diagnosis and treatment, with a complete Desk index
Year: 1920 (1920s)
Authors: Wilson, J. C. (James Cornelius), 1847-1934 Potter, Nathaniel Bowditch, 1869-1919
Subjects: Medicine Diagnosis
Publisher: Philadelphia, London, J. B. Lippincott Company
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uehenne type.Other forms appear, as, for instance, early wasting of the deltoids, supra-and infraspinati, and biceps—the upper arm type. In some rather rareor advanced cases the muscles of the lower limbs are involved. The neckand trunk muscles may also waste. Various deformities occur, such as theclaw hand, or main en griffe, in which the proximal phalanges are over-extended and the distal phalanges are flexed; and the so-called monkeyhand, or Affenhand of the Germans, the main de singe of the French,which is caused by overaction of the long extensor of the thumb, causingthe metacarpal bone to be displaced backw^ard and to lie in the same planeas the metacarpal bones of the fingers. In the lower limbs various formsof club-foot result. As the wasting progresses, loss of power occurs, untilin advanced cases the wasted arms hang powerless at the sides. In the 1 R. T. Williamson: Amyotrophic Lateral Sclerosis and Progressive Muscular Atrophy, EdinburghMed. Journal, April, 1917, p. SOI.
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Fig. 390a.—Progressive muscular atrophy.—Atlas of Clinical Medicine (Dr. B>Tom Bramwell). By courtesy of the author.
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