Peripheral neuropathy is a common presentation on neurology inpatient wards, and may also complicate systemic illness. As such, a systematic approach to diagnosis and management is an important skill. Clinical features of peripheral neuropathy, in particular the time course of symptom evolution, the distribution of clinical involvement, and associated features of systemic disease, provide indicators of the underlying pathophysiological mechanism of nerve dysfunction. Electrodiagnostic studies are indispensable to categorize the neuropathy as predominantly demyelinating or axonal and may also demonstrate specific diagnostic features. Further investigations and management are tailored based on the findings of these initial assessments.
The prevalence of peripheral neuropathy is estimated at 8% of primary care patients more than 55 years of age,1 and this increases to more than 25% of patients with type 2 diabetes mellitus.2 Common causes of neuropathy include diabetes mellitus and neurotoxins such as alcohol, chemotherapy, and other medication, which are frequently encountered in inpatient medical settings, making peripheral neuropathy a common referral for neurological consultation.
The present chapter will use illustrative clinical examples to provide a framework for clinical diagnosis of patients presenting with peripheral neuropathy as well as motor neuron disease (MND), along with a suggested approach to the investigation and management of such patients.
Clinical features of peripheral neuropathy
Patients with peripheral neuropathy present with various combinations of symptoms, including alterations in sensation, pain, muscle weakness, and autonomic symptoms such as postural hypotension and altered gastrointestinal motility. Peripheral neuropathy may be suspected when these symptoms are combined with appropriate signs on clinical examination, such as diminished muscle stretch reflexes and acral sensory loss. It is important, however, to consider other differential diagnoses during the workup, including myelopathy, polyradiculopathy, neuromuscular junction disorders, and myopathy, which may all mimic peripheral neuropathy and MND.
An important initial step in the diagnosis of peripheral neuropathy and MND is identifying clinical patterns that may enable differential diagnoses to be developed. In general, peripheral neuropathy may be categorized based on a number of factors: (1) the rapidity of onset and evolution; (2) the distribution of nerve involvement; (3) the elements of the peripheral nervous system involved; (4) associated neurological features; and (5) associated systemic features.
Electrodiagnosis of peripheral neuropathy
Electrodiagnostic studies are the cornerstone investigation for patients presenting with peripheral neuropathy. Electrodiagnostic studies may include one or more of nerve conduction studies (NCS), electromyography (EMG), repetitive nerve stimulation (RNS), and single-fiber EMG (SFEMG), with NCS and EMG the bulk of studies performed. Additional specific electrophysiological testing, such as evoked potential studies, may also be indicated. Autonomic studies such as sympathetic skin responses, heart rate variability with Valsalva, and quantitative sweat testing may also be of value when evaluating patients with autonomic involvement.