Stiff Person Syndrome Mimicking as
Atypical Parkinson’s Disease - A Diagnostic
Aakash Kodikoppa Somappa1* and Tejashwini Choudhary2
1,2Kasturba Medical College, Manipal, Karnataka, India
Submission: August 29, 2023; Published: September 13, 2023
*Corresponding author: Aakash Kodikoppa Somappa, Manipal Academy of Higher Education, Manipal, Karanataka, India
How to cite this article: Aakash Kodikoppa S, Tejashwini C. Stiff Person Syndrome Mimicking as Atypical Parkinson’s Disease - A Diagnostic Dilemma. Open Access J Neurol Neurosurg 2023; 18(4): 555992. DOI: 10.19080/OAJNN.2023.18.555992.
Stiff person syndrome (SPS) is a rare neurological disorder characterized by stiffness and spasm of the truncal muscles and subsequent postural deformities. In this report, we present a case of a woman in her early 60s who presented to us with muscle stiffness, back pain, and frequent falls. On examination, she was found to have increased muscle tone and mild tremors. Given her age and presentation, a provisional diagnosis of Atypical Parkinson’s was made. Patient was treated with Diazepam. Because of presence of autoimmune co-morbid conditions, anti-glutamic acid decarboxylase (GAD) antibodies were tested, which were positive, and thus, diagnosis of SPS was made. Treatment with Diazepam was continued, and her symptoms significantly improved. Even though SPS is a rare disorder, our case report highlights the need to keep it in differential diagnoses when an elderly patient presents with stiffness and postural instability, as treatment for SPS and atypical Parkinson’s vary considerably.
Keywords: Stiff person syndrome; Atypical Parkinson’s; Anti-GAD antibodies; Rare disorder
Stiff person syndrome is a progressive neurological disease even with treatment and results in significant disability in patients affected . In this case report, we will go over our patient’s presentation, the variants of SPS and the presentation of these variants. We will also discuss Atypical Parkinson’s disease and why this diagnosis was considered in our patient.
The main pathogenesis of SPS is thought to be blockade of glutamic acid decarboxylase (GAD) enzyme which is responsible for maintaining inhibitory pathways in the central nervous system. GAD blockade results in reduced levels of gamma butyric acid (GABA) producing loss of neural inhibition. GAD blockade mainly results from anti-GAD antibodies that are associated with multiple autoimmune disorders, the most commonly associated disease being type 1 diabetes mellitus .
There are several variants of the disease . The classic variant is associated with other autoimmune disorders while the partial SPS is characterized by stiffness limited to only to one limb. Progressive encephalomyelitis with rigidity and myoclonus is another uncommon variant of the disease characterized by transient oculomotor disturbance. Another rare variant of this disease is the paraneoplastic SPS which is suspected in patients who are anti-GAD negative. These patients have antiamphiphysin antibodies and have associated underlying malignancy of the breast and lung.
Classic SPS is the most common variant of the disease and is characterised by the presence of anti-GAD antibodies and presence of autoimmune diseases. The disease presents with muscle stiffness involving the axial group of muscles, lumbar group, and the proximal limb muscles. The disease is progressive and leads to deformities. As the stiffness and rigidity in the axial muscle group progresses, patients also develop a wide based gait and tend to have frequent falls, thus predisposing them to fractures.
Atypical Parkinson’s on the other hand, are a group of neurodegenerative disorders which have features resembling Parkinson’s disease (PD) with additional features that
differentiate them from PD. These include Dementia with Lewy
bodies characterized by the presence of visual hallucinations and
REM sleep behaviour disorder, Multi system atrophy that presents
with postural instability and cerebellar findings like gait ataxia.
Progressive supranuclear palsy is another subtype characterized
by vertical gaze palsy, akinesia, and progressive aphasia. The last
type, called corticobasilar degeneration, is relatively rare and
presents with myoclonus and dystonia .
A common denominator among SPS and Atypical PD is the
presence of rigidity and gait instability producing frequent falls.
Due to the similar features in both diseases, diagnosing them
clinically can be challenging, particularly in older patients. Not all
individuals with Atypical Parkinson’s Disease will exhibit resting
tremors, or bradykinesia during their initial presentation; some
may only display muscle rigidity and postural instability.
A 60-years-old female presented with complaints of backache
and stiffness of 4 months duration which was gradual in onset
and progressive in nature. She also complained of worsening of
stiffness and tightness in her back since the last 2 months and also
gave history of 5 episodes of falls. She also developed difficulty in
getting up from squatting position. Her past medical history was
significant for diabetes mellitus and hypothyroidism for which
she was on regular medications. On examination, her vitals were
stable. Neurological examination findings revealed increased
muscle tone in all four limbs and mild tremors of the hands
were noted. Deep tendon reflexes were exaggerated. Cerebellar
examination did not reveal any findings. In view of progressive
muscular rigidity, tremors and postural instability in an elderly
patient, a provisional diagnosis of Atypical Parkinson’s was made
while keeping Stiff person syndrome in the differential because
of presence of autoimmune conditions diabetes mellitus and
hypothyroidism. Magnetic resonance imaging (MRI) of the brain
and spine were normal. A nerve conduction study was done which
was normal and electromyography was inconclusive.
Serum panel to detect auto antibodies was sent to the lab. The
reports came back positive for anti-GAD antibodies and thus the
conclusive diagnosis of SPS was established.
During her stay in the hospital, patient was treated with tablet
Diazepam 10mg three times daily, which alleviated her symptoms.
Her blood sugars were controlled, and thyroid function tests
were also done, which were normal. Her symptoms significantly
improved following treatment with diazepam, and she was
discharged in stable condition. She will be regularly followed up
on out-patient basis.
A summary of her lab reports can be found in Table 1.
The prevalence of Stiff Person Syndrome is only 1 – 2 people
per million. Though the pathophysiology of the disease is unclear,
neurologists find autoimmunity to be the main culprit, as majority
of the cases are associated with anti-GAD positive antibodies.
While their presence supports the diagnosis, their absence does
not rule out the disease. The disease mainly affects people in their
2nd to 5th decade of life and affects women more than men .
The clinical course is progressive stiffness slowly leading to
deformities and functional impairment. Intellect and memory are
spared. There is no confirmatory test, although anti-GAD antibody
test is widely accepted as the diagnostic test. Imaging is noncontributory,
neurological testing may reveal continuous firing of
action potential. Treatment is usually symptomatic and managing
any co-morbid conditions. Death can result from diaphragmatic
Even though the disease is rare, because of its similarity in
presentation with that of Atypical Parkinson’s, this differential
must be kept in mind, especially in elderly patients.
Hence in elderly patients presenting with gait instability,
frequent falls and muscle rigidity, physicians need to consider
both SPS and atypical PD and ruling out one of them based on the past medical history and lab findings.
Stiff person syndrome being a rare disorder can easily be
missed. It’s prognosis is guarded, and thus early recognition of the
disease and initiation of treatment can slow down the functional
decline in these patients. As the diseases progresses, patients lose
the ability to ambulate and require walking assistance device .
They may also require assistance for activities of daily living, and
this can have a psychological effect on these patients. Providing
psychological counselling is equally crucial to ensure the wellbeing
of individuals, a fact that might be disregarded by physicians
primarily focused on treating the physical aspect of the disease.