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.