Writer's cramp: task-specific hand dystonia, causes and treatment

The NHS defines dystonia as uncontrolled and sometimes painful muscle movements (spasms). It can affect the whole body or just one part, and in the NHS table of types, task-specific dystonia (writer's cramp) is the form that affects the hands, arms and wrists. NHS inform describes writer's cramp as one of the types of focal dystonia that affect a limb, alongside neck dystonia, voice (laryngeal) dystonia and the muscles around the eyes (blepharospasm).

A review of botulinum toxin treatment explains the idea of task-specificity: the dystonic movements or posturing happen within the context of a specific pattern of movement. In writer's cramp the upper limb is affected during the act of writing, and the review describes it as one of the most common forms of focal hand dystonia. GPnotebook, a UK reference for GPs, describes it as tightening of the fingers, hands and forearm while writing.

The NHS lists uncontrolled muscle cramps and spasms, parts of the body twisting into unusual positions and shaking among symptoms of dystonia in general, and says the symptoms may be continuous or come and go and may be triggered by tiredness, stress, alcohol or caffeine, talking, eating or chewing, and activities like writing, typing or playing an instrument.

The botulinum toxin review describes how writer's cramp typically begins: onset is usually insidious and slowly progresses over months, with symptoms beginning when grasping a pen and an alteration of grip, sometimes with the wrist hyper-flexing and difficulty gripping that requires extra force. Handwriting may be difficult to read and the pen may jerk across the paper. It describes simple writer's cramp, where the problem occurs only with writing, and progressive or complex forms in which other manual tasks such as eating, typing and shaving are involved.

The review reports that onset is often in the fourth decade of life, that men are slightly more affected than women, and that a family history is reported in 5 to 20% of patients. It also notes that about 25% of cases may spread proximally or to the other limb, and that spontaneous remissions are rare.

The NHS says dystonia is caused by a problem with the part of the brain that controls movement, and that often it is not known why this happens. It may sometimes be due to an inherited genetic problem, a side effect of certain medicines such as antipsychotics and anti-sickness medicines, Parkinson's disease, stroke, cerebral palsy or multiple sclerosis. NHS inform distinguishes primary dystonia, which is more likely to have a recognised genetic cause and often begins in childhood, from secondary dystonia caused by another condition.

Writer's cramp is a focal form, affecting one part of the body. The review mentions possible genetic variants contributing to focal hand dystonia, and GPnotebook describes it as occurring in someone who has been writing to excess.

The NHS says if your GP thinks you could have dystonia, they will refer you to a neurologist for tests. The neurologist may ask about your symptoms, other conditions and medicines, ask if anyone in your family has dystonia, carry out blood and urine tests and arrange a brain scan to look for any problems. NHS inform says you may need tests to confirm whether you have primary or secondary dystonia.

For writer's cramp, the defining feature described in the review is that the abnormal posture or movement occurs during the specific task of writing, which is why a neurologist will usually ask you to show how you write.

The NHS says the main treatments for dystonia are injections of botulinum toxin directly into the affected muscles, which need to be repeated about every 3 months, medicine to relax the muscles in a larger part of the body, and deep brain stimulation surgery, with physiotherapy and occupational therapy that may also help. NHS inform says that for focal dystonia you might be offered botulinum toxin, with effects lasting around 3 to 6 months, and that you might need to try several options to find which works best.

The botulinum toxin review concludes that injection is presently the most effective therapy for focal task-specific dystonia. Across six controlled studies with 139 patients, 99 of them with writer's cramp, pooled data showed 73% of those who received toxin improved. It notes that choosing which muscles to inject remains an area of active research, and that other options include oral medicines, neuromodulation and surgery.

The NHS also says physiotherapy and occupational therapy may help, and an occupational therapist can discuss practical ways of managing writing tasks.

The NHS says dystonia affects people in different ways, the severity of symptoms can vary from one day to another, it may get worse for a few years but then remain steady, and occasionally it can improve over time. It can have a big effect on daily activities and work. Dystonia UK, the charity named by both the NHS and NHS inform, provides information and support for people living with dystonia.