Autoimmune Neurology Series
A subset of patients diagnosed with PSP or MSA harbour neuronal antibodies and respond dramatically to immunotherapy. A decade of follow-up data now tells us why early identification is everything.
ZX
ZeiniX Life Sciences | Autoimmune Neurology Diagnostics | India
Expert Perspective
When a patient presents with progressive parkinsonian features — bradykinesia, rigidity, postural instability — and fails to respond meaningfully to levodopa, the clinical reflex is to reach for a degenerative label: Progressive Supranuclear Palsy (PSP), Multiple System Atrophy (MSA), or one of the other Parkinson plus syndromes. These diagnoses carry an implicit prognosis of relentless, irreversible progression. For most patients, that prognosis is, unfortunately, accurate.
But not for all of them.
There exists a distinct and underrecognised subset of patients with atypical parkinsonism in whom the underlying aetiology is autoimmune — driven by neuronal antibodies, associated with CSF abnormalities, and, critically, responsive to immunotherapy. These patients can improve. Some recover completely. And unlike the degenerative Parkinson plus syndromes, their condition can be treated — but only if it is first identified.
Phenotypically, they mimic the degenerative Parkinson plus syndromes. There are no clinical features to differentiate between them. The only way to identify them is to look.”
This article draws on the foundational 2016 case series from the Neuroimmunology Laboratory at Amrita Institute of Medical Sciences, Kochi — the first Indian series to formally characterise this condition — and the 10-year follow-up of that same cohort published in 2025, which now provides the longest longitudinal data on immunotherapy outcomes in autoimmune atypical parkinsonism available from an Indian centre.
What Is Autoimmune Atypical Parkinsonism?
Atypical parkinsonism — also called Parkinson plus syndrome — refers to a heterogeneous group of neurological disorders characterised by parkinsonian features alongside additional clinical signs that point away from idiopathic Parkinson’s disease. The hallmarks are poor or absent response to levodopa, and early emergence of features such as postural instability eye movement abnormalities, dementia, autonomic dysfunction, pyramidal signs, and cerebellar involvement.
Autoimmune atypical parkinsonism occupies a specific niche within this spectrum. It is defined by three co-occurring features: the clinical phenotype of atypical parkinsonism, the presence of neuronal antibodies in serum or CSF, and a positive — often dramatic — response to immunotherapy.
10
Indian patients in the original 2016 cohort — all antibody-positive, all immunotherapy-responsive
10 yrs
Follow-up duration in the 2025 study — the longest longitudinal dataset from an Indian centre
100%
Of patients showed improvement in motor scores following immunotherapy initiation
The Clinical Picture: What to Look For
The original cohort comprised ten patients — nine males, one female — with an age range of 49 to 75 years and disease durations ranging from just two months to thirteen years. Their clinical diagnoses at the time of presentation included probable MSA, possible and probable PSP, and several cases of atypical parkinsonism that did not neatly fulfil criteria for any of the established degenerative syndromes.
What distinguished these patients was not a unique clinical phenotype — they looked, at presentation, like any other Parkinson plus patient. What distinguished them was what happened when neuronal antibodies were sought, found, and treated.
Presenting Signs and Symptoms — Either Alone or in Combination
Cortico-basal syndrome with cerebellar signs
Cerebellar and parkinsonian symptoms in combination
Parkinsonism with psychosis
PSP with cerebellar signs
Vocal cord involvement
Autonomic dysfunction
Bladder symptoms
Ataxia, tremor, falls
Slowness and rigidity
Encephalopathy
Eye movement abnormalities
Postural instability
KEY CLINICAL POINTER
A generally poor or absent response to levodopa in the setting of an atypical parkinsonian phenotype should prompt active consideration of an autoimmune aetiology — particularly when symptom onset is subacute, disease duration is shorter than expected, or when CSF shows pleocytosis or elevated protein.
The Antibody Landscape: Known and Uncharacterised
The Uncharacterised Neuronal Antibody: The Most Important Finding No One Is Testing For
Of the ten patients in the original cohort, eight carried new uncharacterised neuronal antibodies, one was positive for LGI1 (leucine-rich glioma-inactivated protein 1) antibody, and one carried both LGI1 and an additional uncharacterised antibody. Importantly, none of the nine uncharacterised neuronal antibodies were identical — each patient’s antibody displayed a distinct immunofluorescence pattern on monkey cerebellum substrate, pointing to a diverse antigenic landscape in this condition.
Four of the ten patients had abnormal CSF — one with pleocytosis, three with elevated protein (ranging from 47.5 to 117.5 mg/dl). CSF abnormality was not a prerequisite for the diagnosis, but its presence in 40% of cases adds further weight to the autoimmune framing.
Nine out of ten patients in the original cohort carried an uncharacterised neuronal antibody. This is not a diagnostic gap — it is the diagnostic reality of autoimmune atypical parkinsonism. The antibody does not need a name to be clinically meaningful. What matters is that it is detected
The predominance of uncharacterised neuronal antibodies is the most important lesson from this dataset. It tells us that a testing approach limited to named, commercially available antibodies will miss the overwhelming majority of seropositive cases. In the Amrita cohort, eight of nine positive uncharacterised antibodies were distinct from one another — each patient’s antibody displayed a unique immunofluorescence binding pattern on neuronal substrate. This diversity underscores a fundamental point: autoimmune atypical parkinsonism is not a single-antibody disease. It is a syndrome defined by CNS autoimmunity, and the breadth of the testing platform determines the breadth of what can be found.
The ZeiniX Autoimmune Parkinsonism panel is specifically designed with this in mind. Alongside a comprehensive set of characterised neuronal antibodies — covering classical paraneoplastic, synaptic, and cell-surface targets well-established in the autoimmune neurology literature — the panel includes dedicated testing for uncharacterised neuronal antibodies by indirect immunofluorescence. This is the same methodology that detected the positive findings in 80% of the Amrita cohort. Without it, those patients would have tested negative. With it, they received a diagnosis and a treatment.
Treatment: What Works and What the Evidence Shows
The treatment protocol applied across both the 2016 series and the 10-year follow-up was consistent and systematic. Intravenous methylprednisolone (IVMP) was used as the acute induction agent, followed by maintenance immunosuppression with either mycophenolate mofetil or azathioprine, with an oral prednisolone taper.
Treatment Protocol
- Induction — IVMP 1 g OD for 5 days
Intravenous methylprednisolone; immediate immunosuppressive effect. All 10 patients showed improvement within the 5-day induction period.
- Maintenance — Mycophenolate Mofetil (1 g BID) or Azathioprine (2–3 mg/kg/day)
Sustained immunosuppression to prevent relapse. Choice between agents based on clinical context and tolerability.
- Oral prednisolone taper — then stopped
6 weeks for patients on mycophenolate mofetil; 12 weeks for those on azathioprine. Tapered and discontinued thereafter.
Outcomes: Short-Term Gains and Long-Term Reality
The immediate response to immunotherapy was, in many cases, striking. After five days of IVMP, the mean UPDRS motor score dropped from 3.1 (±1.10) before treatment to 2.1 (±1.10) — a clinically meaningful shift achievable in days, not months. This kind of rapid improvement in bradykinesia, rigidity, posture, gait, eye movement, and autonomic symptoms within a span of days is not the natural history of any degenerative Parkinson plus syndrome. It is, by contrast, exactly what one would expect from effective immunosuppression in an antibody-mediated condition.
Representative improvements in UPDRS motor scores after 5-day IVMP
100% — complete cure at 7 months
Patient 7
90.2% at 4-month follow-up
Patient 3
87.5% at 1-month follow-up
Patient 4
82.3% immediately post-IVMP
Patient 6
80.7% at 6-month follow-up
Patient 1
51.7% — died 1 month later
Patient 5
Source: Kannoth et al. 2016 cohort data. Bar width represents % improvement in UPDRS motor score from baseline
The 10-Year Picture
The 2025 follow-up of the same ten patients provides a sobering but important long-term view. The Kaplan–Meier survival analysis yielded a mean survival time of 74.7 months and a median of 68 months. Six of the ten patients had died by the time of the 10-year review. Of the four surviving patients, three showed outstanding responses to immunotherapy; one maintained a stable disability score over an extended period.
Continued immunotherapy
mRS 1.8
Mean 9q-mRS at last follow-up for patients who maintained immunotherapy — reflecting sustained functional benefit
Discontinued immunotherapy
mRS 4.4
Mean 9q-mRS at last follow-up for patients who stopped — showing relapse and significant functional decline
Kaplan–Meier mean survival
74.7 mo
Median 68 months; 40% of cases censored in survival analysis
Mean immunotherapy duration
16 mo
Range 1–71 months across the cohort; longer duration correlated with better sustained scores
The most instructive signal in the long-term data is the stark contrast between patients who maintained immunotherapy and those who stopped. Patient 9, who continued immunotherapy throughout his life, maintained consistently high quality of life until he died of age-related causes — a markedly different trajectory from those who discontinued treatment and relapsed. The relapse pattern after stopping immunosuppression closely mirrors what is seen in other autoimmune neurological conditions such as myasthenia gravis and multiple sclerosis.
The initial reduction in UPDRS and mRS scores following immunotherapy is likely due to effective suppression of autoimmune activity. The subsequent increase in these scores may result from the discontinuation or reduction of immunotherapy — emphasising the need for continuous and personalised treatment approaches.
Why Early Identification Transforms Outcomes
The median disease duration before immunotherapy in this cohort was highly variable — from as short as three months to as long as 13 years. Patients who had carried a degenerative label for years before an autoimmune aetiology was considered had, in some cases, spent that entire period without access to a potentially effective treatment. The cost of delayed recognition is measured in disability, dependency, and — in an immunotherapy-responsive condition — lost time during which the immune attack on neural tissue continues unchecked.
The question of why autoimmune atypical parkinsonism remains underdiagnosed is not difficult to answer: it is because neurologists do not routinely test for neuronal antibodies in patients presenting with atypical parkinsonism. The degenerative label is reached for first, and it is often reached for last. Antibody testing is seen as an afterthought, or — worse — is not considered at all.
WHAT CLINICIANS GAIN
A diagnosis that is treatable. A prognosis that can change. An opportunity to prevent progressive, immunotherapy-reversible neurological damage before it becomes permanent.
WHAT PATIENTS LOSE WITHOUT TESTING
Months or years on levodopa that provides no meaningful benefit. Progressive disability attributed to degeneration. Continued antibody-mediated neural injury without immunosuppressive protection.
THE RISK OF STOPPING TREATMENT
The 10-year data shows clearly: patients who discontinue immunotherapy relapse. Mean mRS at last follow-up for those who stopped was 4.4 — severe disability — compared to 1.8 for those who continued.
When Should You Test for Autoimmune Atypical Parkinsonism?
Testing should be considered in any patient presenting with atypical parkinsonism who has one or more of the following features — either alone or in combination.
Indications for Autoimmune Atypical Parkinsonism Workup
- Atypical parkinsonism with poor or absent response to levodopa, particularly when the clinical phenotype does not fit neatly within established PSP or MSA criteria.
- Subacute or rapidly progressive onset of parkinsonian features — a tempo more consistent with inflammatory than degenerative disease.
- Parkinsonian features accompanied by psychosis, encephalopathy, or prominent cerebellar signs — combinations that are unusual in classic degenerative Parkinson plus syndromes.
- Younger patients with atypical parkinsonism, or patients with disease durations shorter than what is typical for the degenerative phenotype being considered.
- Abnormal CSF — particularly elevated protein or pleocytosis — in the setting of a parkinsonian syndrome.
- Patients in whom a diagnosis of Parkinson plus syndrome has been made on clinical grounds but in whom the treating clinician retains diagnostic uncertainty.
The Expanding Landscape of Autoimmune Movement Disorders
The Amrita cohort was among the first to formally document autoimmune atypical parkinsonism as a defined entity. Since 2016, the broader literature on autoimmune movement disorders has expanded considerably. CASPR2 autoimmunity has been reported in association with parkinsonism and ataxia. ANNA-2 (anti-Ri) antibodies have been linked to movement disorder presentations including parkinsonism and brainstem dysfunction. IgLON5 — now recognised as a distinct autoimmune encephalopathy with prominent sleep and movement disorder features — can present with parkinsonian signs. Classical paraneoplastic antibodies including ANNA-1 (anti-Hu), PCA-1 (anti-Yo), and CRMP-5 are associated with movement disorder and extrapyramidal phenotypes in the context of underlying malignancy. Each of these antibodies has a distinct therapeutic and prognostic implication — and each can only be identified if it is specifically tested for.
Yet across all these characterised antibodies, the Amrita data reminds us of a crucial truth: in the majority of patients with autoimmune atypical parkinsonism, the causative antibody will not be one of these named targets. It will be an uncharacterised neuronal antibody, detectable only through broad-substrate immunofluorescence testing capable of capturing novel binding patterns. A testing platform that restricts itself to a fixed menu of named antibodies will produce false-negative results in the very patients who most need a positive finding.
What unites this growing family of conditions — characterised and uncharacterised alike — is the therapeutic implication: these are not degenerative diseases whose course is fixed and irreversible. They are immune-mediated conditions whose trajectory can be altered by appropriate, timely, and sustained immunotherapy. The Amrita 10-year follow-up provides outcome data of a duration and quality rarely available for rare neurological syndromes — and its central message is unambiguous: find the antibody, treat the patient, and keep treating.
Conclusion: A Treatable Condition That Must Not Be Missed
Autoimmune atypical parkinsonism is not rare because it does not exist. It is underdiagnosed because it is not looked for — and, when it is looked for, it is often tested for incompletely. The patients who carry this diagnosis present indistinguishably from those with PSP, MSA, or other degenerative Parkinson plus syndromes. The only way to identify them is systematic, comprehensive neuronal antibody testing that covers not just the established named antibodies, but also the uncharacterised neuronal antibodies that, as the Amrita cohort shows, account for the large majority of seropositive cases.
The 2016 Amrita series established that this is a real and immunotherapy-responsive clinical entity. The 2025 follow-up confirms that the benefits of treatment can be sustained over a decade, and that discontinuation carries a genuine risk of relapse. Together, they make a compelling case: in any patient with atypical parkinsonism, autoimmune testing is not an optional add-on. It is an essential diagnostic step — and the quality of that testing determines the quality of the answer.
The ZeiniX Autoimmune Parkinsonism panel covers the full spectrum of antibodies relevant to this condition — including characterised paraneoplastic, synaptic, and cell-surface antibodies, and critically, dedicated testing for uncharacterised neuronal antibodies. Clinicians with queries about testing in atypical parkinsonism are encouraged to contact their ZeiniX Life Sciences representative.
References
1. Kannoth S, Anandakkuttan A, Mathai A, Sasikumar AN, Nambiar V. Autoimmune atypical parkinsonism — A group of treatable parkinsonism. Journal of the Neurological Sciences. 2016 Mar 15;362:40–46. doi: 10.1016/j.jns.2016.01.006. Epub 2016 Jan 13. PMID: 26944115.
2. Sreelakshmi Sunil Kumar, Kannoth S, Nambiar V, Gopinath S, Anandakuttan A, Saraf Udit Umesh, Unnikrishnan G, Thevarkalam M, Mathai A, Rangaswamy UK, Sudhakar A. Autoimmune Atypical Parkinsonism: A 10 year follow up of the original cohort. Neurological Sciences. Published online 23 January 2025. doi: 10.1007/s10072-025-07995-1.
ZeiniX Life Sciences is India’s dedicated autoimmune neurology diagnostics laboratory. Samples are tested at the Neuro-Immunology Lab, Dept. of Neurology, Amrita Institute of Medical Sciences, Cochin. For sample pick-up and clinical queries, contact Customer Care: +91 8867759300 | support@zeinixlife.com | ZeiniX Life Sciences Pvt. Ltd., Ground Floor, Sy No 27, Degenahalli, Budihal Post, Nelamangala, Bangalore – 562 123.