What are the primary differential diagnoses of Kennedy disease (KD)?

Updated: Sep 30, 2019
  • Author: Paul E Barkhaus, MD, FAAN, FAANEM; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Table 1. Primary Differential Diagnoses of Kennedy Disease (Open Table in a new window)



Differentiating Characteristics or Tests



Upper motor neuron involvement with tendency for distal-greater-than-proximal weakness [58]

Spinal muscular atrophy

See Table 2 below

Fascioscapulohumeral muscular dystrophy

Autosomal dominant pattern with myopathic findings on muscle biopsy and EMG, positive genetic marker

Myasthenia gravis - Adult acquired form

Extraocular muscle frequently involved, EMG consistent with neuromuscular transmission disorder, acetylcholine receptor antibodies frequently positive

Oculopharyngeal muscular dystrophy

Autosomal dominant pattern, late onset, predominant involvement of bulbar muscle with ptosis and mild ophthalmoparesis, EMG and muscle biopsy results consistent with myopathic process, positive genetic marker

Hexosaminidase A deficiency

Rectal biopsy, enzyme assay

Sandhoff disease

Rectal biopsy, enzyme assay

Syphilis (neurovascular form)

Positive serology

Lead neuropathy

Index of suspicion based on potential exposure; anemia; elevated serum, blood, and urine lead levels

Motor neuron disease with macroglobulinemia

Monoclonal gammopathy [59]

Autosomal dominant cerebellar ataxia type I

Amyotrophy occasionally prominent finding in SCAs, particularly types II and III; other clinical and laboratory findings suggest condition other than a pure motor-neuron process; appropriate tests of genetic markers for SCA


Elevated serum creatine kinase, EMG and muscle-biopsy results consistent with inflammatory myopathy

Cervical spondylosis

Rostral cervical segmental myotomes (eg, C5, C6) commonly affected, but pattern on EMG testing is highly localizing; possible pyramidal-tract signs if spondylosis compresses spinal cord at same segmental level; no evidence of lower motor-neuro involvement in legs; imaging (eg, cervical MRI, myelography with low-dose CT) findings correlated with suspected lesion

Facial onset sensory and motor neuropathy (FOSMN syndrome) [60, 61]

Slow progressing, trigeminal-onset sensory loss that may spread to upper limbs and torso, associated with lower motor syndrome with prominent bulbar involvement

Table 2. Patterns of Hereditary Spinal Muscular Atrophies that May Resemble Kennedy Disease (Open Table in a new window)





Bulbar hereditary motor neuropathy affecting lowest 6 cranial nerves (Fazio-Londe disease)

Autosomal recessive, onset in childhood, limbs not affected; when associated with deafness, pattern called Vialleto-van Laere disease, which may be X-linked or autosomal dominant

Scapuloperoneal hereditary motor neuropathy

Variable transmission: dominant, recessive, X-linked; pattern of weakness as described; bulbar muscles spared

Fascioscapulohumeral hereditary motor neuropathy

Autosomal dominant, pattern of weakness as described

Hereditary motor neuronopathy with oculopharyngeal involvement

Described in Japanese individuals; autosomal recessive or dominant; ophthalmoplegia, dysarthria, and dysphagia

Hereditary proximal motor neuropathy

Variable dominant or recessive inheritance; onset usually in first 2 decades; bulbar muscles spared

Hereditary distal motor neuropathy

Usually recessive inheritance; onset usually in first 2 decades; bulbar muscles spared; autosomal-dominant distal spinal muscular atrophy linked to chromosome 7 (same locus as that of hereditary sensorimotor neuropathy type 2D) [62]

*In none of these diseases are results of test for the KD marker positive, and associated endocrinopathy or sensory nerve conduction abnormality should be absent.