Table 3

“MND mimic syndromes”: the main differential diagnoses of MND (modified from Kato et al, 2003, with permission)

Final diagnosisCharacteristic featuresDistinguishing diagnostic features and investigations
Cerebral lesionsFocal motor cortex lesions very rarely mimic MND, but frontal lesions with co-existent cervical or lumbosacral root damage may cause confusionMRI/CT; no EMG evidence of widespread chronic partial denervation (CPD) in limbs
Skull base lesionsLower cranial nerve signs (bulbar symptoms and signs; wasting of tongue, often asymmetrical); seldom significant long tract signs unless foramen magnum involved in additionMRI; CT with bone windows; no EMG evidence of CPD in limbs
Cervical spondylotic myelopathyProgressive limb weakness, but often stabilises, or may be variably progressive; asymmetrical onset; combined UMN and LMN signs in arm(s); spastic paraparesis; occasionally fasciculations in armsPain in root distribution, but pain may not be severe and may resolve quickly; often progression followed by clinical stabilisation; no bulbar involvement; MRI evidence of spinal cord and root compression; evidence of brachial (localised to 1 or 2 segments) CPD on EMG (but patients may have co-existent lumbosacral motor radiculopathy with lower limb CPD)
Other cervical myelopathies
  • Foramen magnum lesions (e.g. Arnold-Chiari malformations; meningioma)

  • Intrinsic and extrinsic tumours

  • Syringomyelia

Progressive weakness; foramen magnum lesions and high cervical cord lesions may be associated with focal (C8/T1) wasting; syringomyelia usually associated with LMN signs and dissociated sensory lossUsually involvement of cerebellar and/or sensory pathways; MRI of head and cervical spine reveal pathology
Conus lesions and lumbosacral radiculopathy; spinal dural fistula Inclusion body myositis (IBM)Progressive mixed UMN and LMN syndromeUsually significant sensory symptoms if not signs; bladder involvement; MRI thoracic and lumbosacral region
Progressive weakness; bulbar symptoms; sometimes respiratory muscle weaknessCharacteristic pattern of weakness and wasting (deep fibres of finger flexors, quadriceps femoris); EMG evidence of myopathy; muscle biopsy definitive test (rimmed vacuoles)
Multifocal motor neuropathy (MMN)Focal asymmetrical onset, often upper limb; pure LMN syndrome; may stabilise for months or years; M:F 4:1Conduction block on nerve conduction studies (NCS); weakness often out of proportion to wasting; positive anti-ganglioside (GM1) antibodies in ,70%; improvement with intravenous immunoglobulin (IVIG) in ,70%
Myasthenia gravisBulbar involvement usually (not always) associated with fatiguability, diplopia, ptosis; no wasting; no UMN signsAnti-acetylcholine or anti-MuSK antibodies; EMG (repetitive stimulation, single fibre EMG)
Benign fasciculation syndromeBenign fasciculations common in calf muscles; fasciculations elsewhere often felt rather than seen and described as localized twitching lasting few seconds; no weakness; patients often health professionals or relatives of people with MNDEMG shows fasciculations without denervation; CPK normal
Kennedy’s disease (x linked bulbar and spinal muscular atrophy)Males symptomatic; slowly progressive bulbar and limb weaknessFamily history; fasciculations of facial muscles; gynaecomastia; proximal symmetrical weakness in addition to foot drop; mild sensory neuropathy on NCS; positive CAG repeat mutation in exon 1 of androgen receptor gene