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Table 2 Differential diagnosis between ALS and KD. The interpretation of these simple criteria must be put in perspective with the phenotypic heterogeneity of these two pathologies and more particularly of ALS (adapted from Pradat, 2014)

From: The French national protocol for Kennedy’s disease (SBMA): consensus diagnostic and management recommendations

Sex and ageKDALS
Adult man in his thirties or fortiesAdult man or woman in their fifties or sixties
GeneticX-linked transmission
Family history found in 2/3 of the cases
Familial in 10% of cases (autosomal dominant, recessive, multigenic, exceptionally X-linked)
Neurologic signs
Limb involvement
Predominance in LL vs UL
Proximal vs distal
LL more affected
Proximal predominance
Most often asymmetrical
Proximal = distal
Pyramidal syndromeAbsentPresent in most patients
Bulbar involvement
FasciculationsLingual quasi constant
lips, chin, or perioral area (often with a myokymic appearance).
Lingual frequent
Lingual atrophyPresent with a reshaped aspectPresent
Dysarthria and dysphagiaModerate, contrasting with the severity of lingual atrophy and slowly progressiveEvolutive (frequent use of assistive devices for communication and enteral nutrition)
Pseudo-bulbar involvementabsentpossible
Cognitive involvementAbsent or very slightAssociation with fronto-temporal dementia in 5–10% of the cases.
Respiratory insufficiencyRareCommon
Normal life expectancy
Rapid (but slow progressive forms)
Median survival of 3 years
ENMGChronic motor denervation associated with a decrease of sensory potentialsMotor denervation with frequent signs of activity (fibrillation) and normal sensory potentials
CPKImportant elevationElevation
  1. Abbreviations: CPK creatine phosphokinase enzyme, ENMG electroneuromyogram, LL lower limbs, UL upper limbs