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What is Focal dystonia and explain in detail?
Focal dystonia, or focal task specific dystonia, is a neurological condition, a type of dystonia, that affects a muscle or group of muscles in a specific part of the body during specific activities, causing involuntary muscular contractions and abnormal postures.  There are many different types of focal dystonia, each effecting a different region of the body.  For example, in focal hand dystonia, or writers cramp, the fingers either curl into the palm or extend outward without control. In musicians, the condition is called musicians focal dystonia, or simply, musicians dystonia. In sports, it may be involved in what is commonly referred to as the yips. The condition appears to be associated with over-training, and individualized treatment strategies may involve medications, retraining techniques, and procedures.

Signs and Symptoms
People with dystonia experience tightness, cramping, fatigue, involuntary sustained or repetitive muscle contractions that can be painless or painful and resulting in abnormal posturing, twisting motions, and even tremors. Focal dystonia typically presents in adults, more commonly in women ranging from ages 30 through 40.  Major types of focal dystonia affect the limbs, face, mouth, neck, and larynx.  These focal dystonias can be exclusive to specific tasks, like writing or playing an instrument.  Focal dystonia will typically have a subtle and slow onset before slowly worsening over years.  During the beginning stages, symptoms can be intermittent and without clear associations and provocation.  The progression of this disease can vary from person to person. During the first couple years of onset, symptoms can partially or completely disappear for days to months, but return in other parts of the body.

Causes
Current medical science does not precisely describe the causes of dystonia, however genetic and environmental factors may play a large role. Misfiring of neurons in the sensorimotor cortex, a thin layer of neural tissue that covers the brain, is thought to cause contractions. This misfiring may result from impaired inhibitory mechanisms during muscle contraction. When the brain tells a given muscle to contract, it simultaneously silences muscles that would oppose the intended movement. It appears that dystonia interferes with the brains ability to inhibit those surrounding muscles, leading to loss of selectivity.The sensorimotor cortex is organized as discrete "maps" of the human body. Under normal conditions, each body part (such as individual fingers) occupies a distinct area on these cortical maps. In dystonia, these maps lose their distinct borders and overlap occurs. Exploration of this initially involved over-training particular finger movements in non-human primates, which resulted in the development of focal hand dystonia. Examination of the primary somatosensory cortex in the trained animals showed grossly distorted representations of the maps pertaining to the fingers when compared to the untrained animals. Additionally, these maps in the dystonic animals had lost the distinct borders that were noted in the untrained animals.
Imaging studies in humans with focal dystonia have confirmed this finding. Also, synchronous afferent stimulation of peripheral muscles induces organizational changes in motor representations, characterized both by an increase in map size of stimulated muscles and a reduction in map separation, as assessed using transcranial magnetic stimulation.The cross-connectivity between areas that are normally segregated in the sensory cortex may prevent normal sensorimotor feedback and so contribute to the observed co-contraction of antagonist muscle groups, and inappropriately timed and sequenced movements that underlie the symptoms of focal dystonia. It is hypothesized that a deficit in inhibition caused by a genetically mediated loss of inhibitory interneurons may be the underlying cause of the deficits observed in dystonia.While usually painless, in some instances the sustained contraction and abnormal posturing in dystonia cause pain. Focal dystonia most typically affects people who rely on fine motor skills—musicians, writers, surgeons, etc. It is thought that the excessive motor training those skills require may contribute to the development of dystonia as their cortical maps become enlarged and begin to overlap. Focal dystonia is generally "task-specific," meaning that it is only problematic during certain activities.

Diagnosis
The diagnosis of focal dystonia is highly dependent on the history of the patient, as physical exam is typically normal, and ruling out other causes of movement disorder. The main types of are blepharospasm, oromandibular dystonia, spasmodic dysphonia, spasmodic torticollis, and limb dystonia, all affecting a different region of the body. Labs and imaging may be ordered as workup to evaluate for other causes of dystonia. Focal dystonias involving  are commonly misdiagnosed A provider can consider to rule in or out Dopamine-responsive dystonia with a levodopa trial.

Treatment
Treatment options would be based on the type of focal dystonia the patient has. If possible, incorporating rest earlier to symptom onset has shown to have greater improvement in symptoms for Writers cramp.

Physical Therapy
Physical therapy is commonly used as an adjunct or main form of treatment for focal dystonia, however more studies for its benefit are needed.  Bass guitarist and instructor Scott Devine said that he wears a glove while playing bass guitar because of the condition. He finds that the glove stops the involuntary finger movements. He says it works for him but does not suggest that it may work for everyone with the condition.

Medications
Anticholinergics such as Artane can be prescribed for off-label use, as some patients have had success. Benzodiazepines, such as Clonazepam, can be used as a muscle relaxant. Other oral medications have been studied for different types of focal dystonia, such as baclofen, tetrabenazine, amantadine, antipsychotics, and amphetamine

Procedures
This condition is often treated with injections of botulinum neurotoxin type A (BoNT/A). BoNT/A reduces the symptoms of the disorder but it is not a cure for dystonia. Since the root of the problem is neurological, doctors have explored sensorimotor retraining activities to enable the brain to "rewire" itself and eliminate dystonic movements. The work of several doctors such as Nancy Byl and Joaquin Farias has shown that sensorimotor retraining activities and proprioceptive stimulation can induce neuroplasticity, making it possible for patients to recover substantial function that was lost to focal dystonia. For some dystonias, Deep brain stimulation may be considered where BoNT treatment fails. If the dystonia is cause by an underlying nerve entrapment, surgical decompression has shown to have improvement in some cases.

Prognosis
Recovery from focal dystonia has varying results, ranging from minimal improvement in function to complete recovery and ranging from weeks to years.

Prevention
Though studies on prevention of focal dystonia is limited, it is believed for musicians dystonia that mindfulness of muscle use and proper rest can help prevent focal dystonia and injury.

Performing Arts Medicine
Musicians Dystonia
Musicians dystonia treatment studies have yielded varying results. This condition can often be misdiagnosed as psychogenic, as this was previously thought to be its cause. In this population, men are affected more than women from 20 to 60 years of age. Evaluation of musicians dystonia should include history before and after symptom onset and observation of playing the instrument, as deficits can be subtle and considered minor to the general population. Treatment modalities available, such as BoNT/A, leave many musicians unsatisfied due to muscle weakness and lack of improvement in muscle control. In musicians, this is commonly associated with overuse or high volume of practicing. Though musicians dystonia presents initially as task-specific, one study found that the dystonia can progress outside of playing their instrument.Treatments such as splinting and sensorimotor retraining for focal hand dystonia have shown to be beneficial with varying results. It is important to consider the mental health and social aspect of this condition as a musicians self-identity and career can be affected considerably