Stiff-person syndrome: what it is, symptoms, causes and diagnosis

Stiff-person syndrome (SPS) is a rare neurological condition. The Brain Charity explains that it affects the brain and spinal cord and is defined by muscle stiffness, rigidity and body spasms, which can be brought on by heightened sensitivity to stimuli such as sudden noise or light. It lists other names including stiff man syndrome and progressive encephalomyelitis with rigidity and myoclonus (PERM).

Royal Cornwall Hospitals NHS Trust describes it as a rare disorder characterised by progressive fluctuating muscular rigidity and spasms, strongly associated with other autoimmune disease.

The Brain Charity lists the main symptoms of stiff-person syndrome. It adds that having these symptoms can also lead to anxiety and depression, and that it can feel isolating and challenging to live with.

The US National Institute of Neurological Disorders and Stroke (NINDS) notes that stiffness often affects the torso, arms and legs, that people can develop hunched postures, and that noises such as a car horn can trigger spasms and falls. It says symptoms may range from one area of the body to a widespread syndrome. This is a non-UK source and is used for context only.

• Stiff and rigid muscles.

• Muscle and body spasms, often triggered by sudden noise, light or touch.

• A slouched or hunched posture.

• Weight loss.

• Anxiety and depression, which can develop as a result of living with the symptoms.

The Brain Charity says the cause is unknown, but research shows it may be due to an abnormal autoimmune response in the brain and spinal cord, which is when the immune system attacks the body. It is also associated with other autoimmune diseases such as vitiligo.

Leeds Teaching Hospitals NHS Trust notes that GAD antibodies are associated with both type 1 diabetes and stiff-person syndrome, and that SPS can co-exist with type 1 diabetes. The Brain Charity says SPS affects about twice as many women as men, with symptoms commonly noticed between the ages of 30 and 60.

A neurologist makes the diagnosis based on symptoms, examination and tests. NINDS says SPS is often misdiagnosed as Parkinson's disease, multiple sclerosis, fibromyalgia or anxiety because it is rare and little understood, and that an MRI of the brain and spinal cord and electromyography may be done to rule out other causes.

Antibody blood tests are central. Royal Cornwall Hospitals describes a UKAS-accredited GAD antibody test on a blood sample. Leeds Teaching Hospitals says the presence of anti-GAD antibodies can confirm the clinical diagnosis, that 60 to 70% of people with SPS have them, and that false positives may occur where type 1 diabetes is present and the diagnosis of SPS is not clear. Glycine receptor antibodies are found in people with SPS who are usually GAD antibody negative, and in related syndromes.

The Brain Charity says treatment can help manage symptoms. It might be provided through medication such as muscle relaxants, as well as physical therapy and lifestyle changes.

NINDS says several symptoms improve with benzodiazepines such as diazepam, and with other medicines that relax muscles or relieve spasms such as baclofen, gabapentin, dantrolene and tizanidine. It also reports that a trial funded by NINDS showed intravenous immunoglobulin (IVIg) reduced stiffness and sensitivity to noise, touch and stress, and that people may benefit from speech and physical therapy.

Because SPS is rare, treatment is best led by a neurologist with experience of the condition, and plans differ between people. There is no cure, and ongoing review is needed.

The Brain Charity offers practical help on all aspects of living with stiff-person syndrome, emotional support including counselling, phone befriending and group therapy, and social activities, from its centre in Liverpool for people from all over the UK. It also supports carers, friends and family.

Triggers such as sudden noise can make leaving the house difficult, so planning, adaptations and support from occupational therapy and physiotherapy can help. Anxiety and depression are common and are worth raising with your care team.

See your GP if you have persistent muscle stiffness, painful spasms or falls that have no clear cause, so that you can be referred to a neurologist. If you have been diagnosed and have a fall with injury, severe spasms that do not settle, or difficulty breathing or swallowing, seek urgent help through NHS 111, A&E or 999.

On the NHS, SPS is usually diagnosed and managed by a neurologist, sometimes at a specialist or neuroimmunology centre, with blood tests handled by hospital immunology laboratories. Private neurology review may offer quicker access to assessment or a second opinion, but prescribing of treatments such as immunoglobulin is usually coordinated through NHS specialist services. Ask your team how care is shared with your GP.