Avoiding false positive diagnoses of motor neuron disease: lessons from the Scottish Motor Neuron Disease Register.

OBJECTIVES: To describe the frequency and characteristics of those patients initially registered with the Scottish Motor Neuron Disease Register (SMNDR) but who subsequently had a diagnosis other than MND made (false positives), to analyse the features which led to a revised diagnosis, and to draw conclusions which might improve routine neurological practice.
METHODS: The Scottish Motor Neuron Disease Register is a community based, prospective disease register to identify and follow up all incident cases of motor neuron disease in Scotland. Fifty three patients out of a total of 552 registered are presented, who, after initial registration, were later excluded because they failed to satisfy the register's diagnostic criteria.
RESULTS: Seven of these patients were labelled as "MND plus" syndromes and may represent a distinct subset of MND. The remaining 46 patients had an alternative diagnosis made (false positive group), accounting for 8% of the total. In half of these cases, potentially beneficial therapies are available. The predominant reasons which lead to a diagnostic revision were: failure of symptom progression, development of atypical clinical features for MND, and investigation results.
CONCLUSIONS: Patients with MND should undergo thorough and relevant investigations at presentation with the emphasis on neuroradiological imaging and neurophysiology; all patients should be followed up by an experienced neurologist, particularly those in whom symptoms and signs are restricted to either the bulbar or spinal muscles; failure of symptom progression or development of atypical features should lead to an early reassessment; finally, patients should be informed of the diagnosis only when it is secure.