11th August 2024

Diagnosis of MND

Electromyography (EMG) and nerve conduction studies (NCS) are the most useful investigations in the diagnosis of motor neuron disease. Findings include:

• Evidence of widespread denervation
• Preservation of motor conduction velocity

The exception is primary lateral sclerosis, as this typically only involves the upper motor neurons.

Differentials to consider

Key differentials for motor neuron disease include:

• Cervical radiculopathy – may present with sensory symptoms as well; MRI will show disc compression
• Syringomyelia – loss of sensitivity to pain or temperature, primarily in the upper limbs; MRI will show a fluid-filled syrinx
• Motor neuropathies, e.g. multifocal motor neuropathy (MMN) – both MMN and MND present with progressive pure motor weakness. MMN only has LMN weakness, and the progression of weakness is typically slower than in MND. Additionally, NCS will differentiate between MND and MMN: in MMN there will be a conduction block, however motor nerve conduction velocities are preserved in MND
• Inflammatory myopathies, e.g. inclusion-body myopathy – muscle biopsy and EMG will differentiate these from MND. EMG can confirm the presence of a myopathy and identify a muscle biopsy site. Additionally, patients with MND, depending on the pattern of weakness (UMN vs LMN), will show abnormal electrical activity in their muscles, e.g. fasciculations, which will be recorded on an EMG

Staging and  management of MND

There is no formal staging for MND. However bulbar presentations have been associated with a poorer prognosis as respiratory muscles are involved earlier, and patients are generally dependent on parenteral nutrition and have a high risk of aspiration. Death is usually within 1 to 5 years of diagnosis.

Management is guided by a multidisciplinary team. Discussions around the ceiling of care should be had early, including patient preference for the use of non-invasive ventilation. Additionally discussions surrounding long-term feeding options are also best had early in the disease course. Long-term PEG (percutaneous endoscopic gastrostomy) or RIG (radiologically inserted gastrostomy) feeding is often recommended, especially if the patient has bulbar weakness.

Riluzone is the only pharmacological treatment currently licensed for MND and has been shown to increase average survival by 2-3 months.