Achondroplasia Clinical Presentation
- Author: Shital Parikh, MD; Chief Editor: Jeffrey D Thomson, MD more...
Gross motor development frequently is delayed. Motor milestones (eg, head control and independent sitting, standing, and ambulation) may lag by 3-6 months. Speech and language problems may be caused by tongue thrust (due to an abnormal maxillomandibular relationship) but often resolve spontaneously. Some 20% of patients experience delayed speech acquisition. Cognitive skills are preserved, and the intelligence level is within normal limits. Cranial enlargement and poor head control place the infant at risk for extension injuries.
An Australian study assessed the functional milestones of achondroplasia children aged 3-7 years. The data showed that whereas milestones were delayed across all ages studied, functioning improved between the ages of 3 and 5 years, though not subsequently. Access to clinicians skilled in achondroplasia management may assist these children to become more independent.[13, 14]
Standing height is below the third percentile for both sexes. The mean adult standing height for men is 132 cm (52 in.), and that for women is 125 cm (49 in.). Sitting height, a reflection of trunk length, is within normal limits.
About 75% of patients have otitis media when younger than 5 years. Recurrent otitis media is common because of poor drainage of the eustachian tubes from underdevelopment of the midface, relative hypertrophy of tonsils and adenoids, and temporal bone abnormalities. Conductive hearing loss is present due to ossicular chain stiffness, and may be either congenital or acquired as a result of recurrent otitis media. Sensorineural hearing loss may be present in a few patients. Maxillary hypoplasia may lead to dental crowding and malocclusion.
Upper-airway obstruction, small chest wall, pectus excavatum, and neurogenic effects from brainstem compression reduce the vital capacity. Incidence of pneumonia, cyanotic spells, apnea, and other respiratory complications is increased. Symptoms of airway obstruction include snoring and sleeping with the neck in a hyperextended position.
Abnormal development of the base of the skull results in a foramen magnum that is smaller than in average individuals. Narrowing of the foramen magnum compresses the cervicomedullary region, causing symptoms of respiratory insufficiency, apnea, cyanotic episodes, feeding problems, quadriparesis, and sudden death. These symptoms are common in the first several years of life because of the failure of the anticipated enlargement of foramen magnum during infancy and childhood. Chronic brain stem compression also may be a cause of hypotonia observed in the first 2 years of life.
Stenosis of the spinal canal and intervertebral foramen leads to symptoms such as low back pain, leg pain, dysesthesia, paresthesia, paraparesis, incontinence, and neurogenic claudication. Claudication may present as vague symptoms of aching or tiredness of the lower extremities induced by walking or standing. Symptoms may progress with a sensation of tingling and numbness and, eventually, weakness. Often, the pain is alleviated if the patient assumes a squatting position or bends forward.
More than 50% of patients experience symptoms of lower-extremity radiculopathy from nerve root compression or cauda equina syndrome. The mean age of onset of back or lower extremity symptoms is 26 years; one third of patients are younger than 15 years at onset.
Symptoms due to abnormal curvature of the spine (eg, kyphosis, lordosis, or scoliosis) may be present, such as deformity, back pain, respiratory dysfunction, neurologic involvement, or symptoms of spinal stenosis. The incidence of kyphoscoliosis may be as high as 33-50% in adults. However, the curve magnitude is generally less than 30° and generally does not necessitate treatment.
Joint laxity may be present in children. Genu recurvatum is common. As the child grows, genu varum (tibial bowing) and lateral tibial torsion become apparent.
Macrocephaly represents ventriculomegaly or arrested hydrocephalus.
Mild but annoying neurologic disturbances can be attributed to local anatomic abnormalities and abnormal stretching of nerves. Examples include hip and knee pain from meralgia paresthetica, ankle pain from irritation of the peroneal nerve, or facial pain due to trigeminal neuralgia.
Achondroplasia is evident at birth as a disproportionate short-limb dwarfing condition (see the image below). Characteristics include an enlarged neurocranium, frontal bossing, flattening of the nasal bridge, midface hypoplasia, and a relatively prominent mandible. The anteroposterior diameter of the chest is flattened, the lower ribs are flared, and the abdomen protrudes.
Before walking, the child has a thoracolumbar kyphosis and lordosis in the interscapular thoracic region. The kyphosis can be severe in the sitting position and may not reduce completely in the prone position. Once independent ambulation is established, an exaggerated lumbar lordosis with forward rotation of the pelvis develops, and the spinal deformity is associated with hip flexion contractures and a prominent abdomen and buttocks. However, some degree of kyphosis persists in 25% of adults.
Upper-extremity involvement is rhizomelic, with the proximal segments more severely affected than the distal segments. The shoulders appear broad because of the normal development of clavicle and well-developed musculature. The short arms may contribute to bulky muscle mass and apparent increased strength in such individuals. Loss of full extension of the elbow, in the range of 15-30°, is present. A trident hand is common and is characterized by a persistent space between the long and ring fingers when approximation of the fingers is attempted in full extension. The fingertips reach the level of the hips, which causes difficulty with hygiene and dressing.
Lower-extremity involvement is rhizomelic, with hip flexion contractures, ligamentous laxity and external rotation of the extremity, and genu recurvatum before walking age. The tibia is bowed, resulting in significant genu varum and some degree of ankle varus. Frequently, gaping of the lateral compartment or lateral translation of the tibia on the femur can be seen during the stance phase. Occasionally, a valgus deformity may develop. The gait is usually a waddling gait, and circumduction motion of the hips and lower extremities occurs when running is attempted.
Spinal deformities are the most common and potentially disabling problems.[16, 17, 18] Spinal canal stenosis and stenosis of the intervertebral foramen are secondary to short thickened pedicles, interpedicular narrowing, thickened laminae, intervertebral disc herniation, degenerative spondylolysis, excessive lumbar lordosis, or anterior wedging of the vertebral bodies from thoracolumbar kyphosis. Sensory deficits, posterior column dysfunction, lower and upper motor neuron signs, and signs of neurologic claudication may be present. Signs of lower-extremity radiculopathy from nerve root compression or cauda equina syndrome are present in more than 50% of patients.
Macrocephaly is present as a consequence of triventricular enlargement and hydrocephalus. However, intracranial pressure is not elevated significantly. In infants, a rough estimate of the pressure can be made by palpating the fontanelles.
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