Clinical Information

Peripheral neuropathy and distal myopathy are well-established inherited neuromuscular disorders characterized by progressive weakness and atrophy of the distal limb muscles.

Inherited peripheral neuropathies are common neurologic disorders that represent a spectrum of diseases with different etiologies. Based on the pattern of inheritance and nerve conduction studies, there are 3 major categories of inherited peripheral neuropathies with isolated nerve involvement. The first group is hereditary motor and sensory neuropathy, also referred to as Charcot-Marie-Tooth (CMT) disease. Individuals with CMT typically present with slowly progressive muscle weakness and atrophy primarily affecting the distal extremities. The second group is hereditary sensory and autonomic neuropathy (HSAN) or hereditary sensory neuropathy if autonomic dysfunction is absent. They predominantly feature slowly progressive loss of multimodal sensation and autonomic dysfunction, with the most common features of HSANs being the loss of sensation of pain and temperature. The third group is distal hereditary motor neuropathy, which is characterized by length-dependent lower motor neuron dysfunction. The clinical phenotype is variable but includes progressive weakness and atrophy of the distal muscles, foot deformities, and decreased reflexes. Inherited peripheral neuropathies may also show involvement of the central nervous system (brain or spinal cord), as in hereditary spastic paraplegia with neuropathy or be part of a systemic syndromic or metabolic disorder. It is important to note that this assay includes testing for TTR-associated with familial amyloidosis.

Distal myopathies are characterized by distal weakness and atrophy that starts in the muscles of the hands or feet and lack of cranial involvement or sensory loss. Distal myopathies are classified based on clinical features, inheritance pattern, and histopathological findings, such as the presence of rimmed vacuoles. Categories of distal myopathies include late adult-onset autosomal dominant forms, adult-onset autosomal dominant forms, early-onset autosomal dominant forms, early-onset autosomal recessive forms, and early adult-onset autosomal recessive forms. Additionally, inclusion body myositis presents with distal muscle weakness and may be in the differential with the distal myopathies.

Given the considerable overlap in clinical phenotype of various disorders with distal weakness, multigene panels can be an efficient and cost-effective way to establish a molecular diagnosis.