Neuromuscular symptoms associated with all forms of NBIA share several descriptive terms. Dystonia describes involuntary muscle cramping that may force certain body parts into unusual, and sometimes painful, movements and positions. Choreoathetosis is characterized by involuntary, rapid, jerky movements (chorea) occurring in association with relatively slow, sinuous, writhing motions (athetosis).
In addition, there may be stiffness in the arms and legs because of continuous resistance to muscle relaxing (spasticity) and abnormal tightening of the muscles (muscular rigidity). Spasticiy and muscle rigidity usually begin in the legs and later develop in the arms. As affected individuals age, they may eventually lose control of voluntary movements. Muscle spasms combined with decreased bone mass can result in bone fractures (not caused by trauma or accident).
Dystonia affects the muscles in the mouth and throat, which may cause poor articulation and slurring (dysarthria) and difficulty swallowing (dysphagia). The progression of dystonia in these muscles can result in loss of speech as well as uncontrollable tongue-biting.
Specific forms of dystonia that may occur in association with NBIA include blepharospasm and torticollis. Blepharospasm is a condition in which the muscles of the eyelids do not function properly, resulting in excessive blinking and involuntary closing of the eyelids. Torticollis is a condition in which there are involuntary contractions of neck muscles resulting in abnormal movements and positions of the head and neck.
Most forms of NBIA involve eye disease. The most common problems are retinal degeneration and optic atrophy. The retina is a thin membrane that lines the back of the eyeball; it helps the eye perceive an image and send it into the brain. In NBIA, early signs of retinal degeneration may be poor night vision or tunnel vision. It can eventually cause significant loss of vision.
Optic atrophy affects the optic nerve, which sends messages between the retina and the brain. The optic nerve is like a cable with thousands of tiny electrical wires that each carry some visual information to the brain. When the nerve is damaged or breaks down, vision can become blurry, side vision or color vision may be abnormal, the pupil may not work properly, or there may be decreased lightness in one eye compared to the other. Eventually, optic atrophy can cause blindness.
Most forms of NBIA involve delays in development with motor skills (movement), and some, such as BPAN, the most common form of NBIA, also frequently have intellectual delays. Cognitive decline may also occur in some of the later-onset forms of NBIA. Although intellectual impairment has often been described as a part of the condition for all NBIA disorders in the past, it is unclear whether this is a true feature for some subtypes of NBIA disorders. Intellectual testing may be hampered by the movement disorder; therefore, newer methods of studying intelligence are necessary to determine if there are cognitive problems.
Seizures occur in some forms of NBIA and may need to be treated with anticonvulsants.