Progressive supranuclear palsy (PSP) is a rare brain disorder that affects approximately 6 in 100,000 people worldwide. It is a rare disease that may appear similar to some other neurodegenerative disorders, in particular Parkinson’s disease, which may make it difficult to diagnose.
PSP causes muscle weakness (“palsy”) and gradually affects gait, balance and overall movement. It causes the patient’s mood, cognitive skills and behavior to deteriorate over time. It was first distinguished from Parkinson’s disease in 1963 as “Steele-Richardson-Olszewski syndrome”.
Progressive Supranuclear Palsy (PSP) Diagnosis
There is no single test that can be performed to identify PSP, and the diagnosis is made on the basis of the symptoms experienced by the patient. This is why a thorough medical examination is crucial to arrive at the right diagnosis. In the USA, the clinical criteria of the National Institute of Neurological Disorders and Stroke and the Society for PSP (NINDS-SPSP) are the most commonly used criteria for the diagnosis of PSP.
The NINDS-SPSP criteria require:
- Difficulty gazing downwards, followed by difficulty gazing upwards (“vertical supranuclear gaze palsy”) caused by the weakening of extraocular muscles
- Loss of balance and lack of coordination (“prominent postural instability”)
- Incidence of falls in the first year of the condition occurring
In 2017 the Movement Disorder Society (MDS) proposed new criteria for diagnosing PSP. They include a list of criteria that should aid a qualified professional to give the right diagnosis. The criteria include both “inclusive” and “exclusive” factors, meaning a list of features that should and should not appear for the condition to be classified as progressive supranuclear palsy. For example, the incidence of falls in the first year of the condition is one of the main symptoms that distinguish PSP from Parkinson’s disease. Again, tremors (shaking) are absent in PSP, in contrast to Parkinson’s.
Radiological Methods in PSP Diagnosis
A magnetic resonance imaging (MRI) brain scan, sometimes followed by a PET scan, may be advised in order to determine which areas of the brain are affected by the disease. An MRI scan is used to form pictures of the soft tissue that makes up the brain. A PET scan may be run, additionally, as it portrays the metabolic processes in the brain as well.
Some areas of the brain that typically show signs of atrophy and degeneration visible on an MRI scan include:
- the midbrain
- the red nucleus
- the quadrigeminal plate
- the pons and cerebellum
An enlargement of the aqueduct and third ventricle, and a signal increase in the inferior olives, may be present as well.
Differentiating between PSP and other disorders
When diagnosing a patient who has PSP, it is important for the doctor to differentiate it from other disorders which may exhibit a number of overlapping symptoms.
Neurodegenerative disorders and other conditions that may appear similar to progressive supranuclear palsy include:
- Parkinson’s disease
- Multiple system atrophy (MSA) of the Parkinsonian type
- Pick’s disease
- Corticobasal ganglionic degeneration (CBGD)
- Microvascular disease of the brain stem
- Tumors of the midbrain area
Some distinct features of PSP that aid in arriving at the right diagnosis include:
- no tremors (shaking)
- difficulty with focusing the gaze, particularly looking down (downward palsy)
- very little or no response to medications typically used in Parkinson’s disease
Four certainty levels have been specified for the diagnosis of PSP, ranging from definitive PSP to clinical symptoms suggestive of PSP that may suggest an early or subtle onset of PSP.