To identify the clinical factors and type of cognitive errors that result in the misdiagnosis of Amyotrophic Lateral Sclerosis (ALS).

Symptom onset of ALS is highly variable making the diagnosis difficult.  In this study, we identified clinical factors and type of cognitive errors that resulted in misdiagnosis of ALS.

88 ALS patients (2011-2017) with at least 1 year follow up were analyzed. Demographic information and clinical characteristics of ALS were reviewed. If a patient received an incorrect diagnosis, type of diagnostic error, clinical factors contributing to the misdiagnosis were recorded. Diagnostic errors were categorized according to Patient Safety Network’s categories of cognitive bias. Statistical analysis was done using Fischer’s Exact test.

20 out of 88 patients received a diagnosis other than ALS in this cohort. Average age is 59.55+/- 1.7, 12 were male, and 16 were Caucasians. Average duration of symptoms prior to diagnosis was 19.25+/-2.71 months, average ALSFRS-R score was 26+/-1.33.  In lower limb-onset ALS (30%), the absence of upper motor neuron (UMN) signs, presence of sensory symptoms, and imaging changes of neuroforaminal or spinal stenosis led to misdiagnosis. In upper limb onset ALS (25%), the presence of split hand sign, clinical signs and symptoms of carpal tunnel syndrome led to misdiagnosis. In bulbar onset ALS (33%), the absence of tongue fasciculations and lack of clinical signs of ALS in the limbs led to misdiagnosis. Lumbosacral radiculopathy, ulnar neuropathy at elbow and myasthenia gravis were the common misdiagnosis (lower limb, upper limb, and bulbar onset respectively). Anchoring heuristic was the most common cognitive bias for misdiagnosis in lower limb, whereas as availability bias was the most common for upper limb and bulbar onset (p<0.05).

Absence of UMN signs, tongue fasciculations and the presence of sensory symptoms, MRI abnormalities, and a split hand sign are common causes of ALS misdiagnosis.