Nemaline myopathy (also called rod myopathy or nemaline rod myopathy) is a congenital, often hereditary neuromuscular disorder with many symptoms that can occur such as muscle weakness, hypoventilation, swallowing dysfunction, and impaired speech ability. The severity of these symptoms varies and can change throughout one's life to some extent. The prevalence is estimated at 1 in 50,000 live births. It is the most common non-dystrophic myopathy. "Myopathy" means muscle disease. Muscle fibers from a person with nemaline myopathy contain thread-like rods, sometimes called nemaline bodies. While the rods are diagnostic of the disorder, they are more likely a byproduct of the disease process rather than causing any dysfunction on their own. People with nemaline myopathy (NM) usually experience delayed motor development, or no motor development in severe cases, and weakness may occur in all of the skeletal muscles, such as muscles in the arms, legs, torso, neck flexors, throat, and face. The weakness tends to be more severe in the proximal muscles rather than the distal muscles. The ocular muscles are normally spared. This systematic review analyzed 55 pediatric case reports published from 2010–2020 to understand genetic, clinical, and pathologic patterns. Presentation of NM varied widely, however, common features in the children included neonatal hypotonia, respiratory distress, delayed motor development, and spinal deformities. The disorder is often clinically categorized into groups with wide ranges of overlapping severity, from the most severe neonatal form which is incompatible with life, to a form so mild that it may not be diagnosed since the person appears to function at the lowest end of normal strength and breathing adequacy. Sporadic late-onset nemaline myopathy (SLONM) is not a congenital disorder and is considered a different muscle disease from NM, which has its onset at birth or early childhood. Respiratory problems are usually a primary concern for people with all forms of NM, and respiratory infections are quite common. NM shortens life expectancy, particularly in the more severe forms, but aggressive and proactive care allows most individuals to survive and even lead active lives. Nemaline myopathy is one of the neuromuscular diseases covered by the Muscular Dystrophy Association in the United States.
Signs and symptoms Signs vary from person to person. Young children and babies lack movement and have a difficult time eating and breathing. For young children not diagnosed immediately at birth, these are usually the first visible symptoms. One sign is a swollen face in disproportional areas. Other examples in newborns include swaying and a difficulty in moving. Other symptoms include feeble muscles in the neck and upper rib cage area. In adults, the most common symptom is respiratory problems. Other symptoms in adults could range from mild to severe speech impediments. It is common to be diagnosed with scoliosis in relation to nemaline myopathy. As babies that have NM develop and become of age when they should start walking, many take longer than average due to the lack of muscle, or just muscle fatigue. Since facial muscles are involved in NM takeover, elongated faces and a lower mandible are often observed in people with NM. People affected by NM usually will begin to feel muscle exhaustion between ages 20–50. NM is usually not progressive. Gastroesophageal reflux, although not common, is associated with NM. Heart abnormalities can occur as a result of NM, but the likelihood of that happening are not high.
Mobility and orthopedics Most children with mild NM eventually walk independently, although often at a later age than their peers. Some use wheelchairs or other devices, such as walkers or braces, to enhance their mobility. Individuals with severe NM generally have limited limb movement and use wheelchairs full-time. Due to weakness in the trunk muscles, people with NM are prone to scoliosis, which usually develops in childhood and worsens during puberty. Many individuals with NM undergo spinal fusion surgery to straighten and stabilize their backs. Although patients early on often have mobility in their joints that is past the normal range, as they age, joint deformities and scoliosis usually occur. If the person with nemaline myopathy keeps an eye on his or her joints early on, the problems with them can be detected when they begin and their progression can be delayed. Treatment of joint problems ranges from stretching exercises with physical therapy to surgical introduction of braces. The benefits of exercise in people with nemaline myopathy are still being studied, however, researchers have seen improvements in muscle function from low-intensity exercise. Vigorous exercise and the use of heavy weights should be avoided.
Respiratory involvement Attention to respiratory issues is critical to the health of many people with NM. Infants with severe NM frequently experience respiratory distress at or soon after birth, although this is only found in the rarest forms. Though respiratory compromise may not be immediately apparent in people with intermediate or mild NM, it often, but not always, exists to some extent. As in many neuromuscular disorders, hypoventilation can begin insidiously, and it may cause serious health problems if not remedied by the use of noninvasive mechanical devices to assist breathing, particularly at night.
Communication and eating Bulbar (throat) muscle weakness is a main feature of nemaline myopathy. Individuals with the most severe forms of NM are unable to swallow and receive their nutrition through feeding tubes. Most people with intermediate and mild NM take some or all of their nutrition orally. Bulbar muscle impairment may also lead to difficulty with communication. People with NM often have hypernasal speech as a result of poor closure of the velopharyngeal port (between the soft palate and the back of the throat). This may be able to be surgically corrected. Communicative skills may be enhanced through speech therapy, oral prosthetic devices, surgery, and augmentative communication devices. NM does not have any impact on cognition or intelligence.
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