Spinobulbar muscular atrophy can mimic ALS: The importance of genetic testing in male patients with atypical ALS

The clinical presentation of amyotrophic lateral sclerosis (ALS) is variable and overlaps with that of other motor neuron diseases such as spinobulbar muscular atrophy (SBMA; Kennedy disease). With the identification of disease-specific mutations such as the CAG repeat expansion in the androgen receptor in SBMA, an accurate molecular diagnosis can be made in some patients with motor neuron disease. To determine the extent of misdiagnosis of ALS we screened 147 male ALS patients and 100 unrelated male patients from 100 familial ALS (FALS) kindreds for the presence of the SBMA mutation using polymerase chain reaction methods. We show that ALS was clinically misdiagnosed in 2% of sporadic cases and in two of the 100 FALS kindreds. This study underscores the difficulty in distinguishing SBMA from ALS clinically, particularly in patients who lack the classic signs of each disease.