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Year : 2022  |  Volume : 25  |  Issue : 6  |  Page : 1235-1236

“Neuroleptic malignant syndrome (NMS) sans rigidity”……Does it exist??

Department of Neurology, Princess Esra Hospital, Deccan College of Medical Sciences, Hyderabd, Telangana, India

Date of Submission07-Jul-2022
Date of Decision04-Sep-2022
Date of Acceptance06-Sep-2022
Date of Web Publication3-Dec-2022

Correspondence Address:
Reshma Sultana Shaik
Department of Neurology, Princess Esra Hospital, Moghulpura, Hyderabad - 500 002, Telangana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aian.aian_593_22

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How to cite this article:
Shaik RS, Manorenj S, Rao RV. “Neuroleptic malignant syndrome (NMS) sans rigidity”……Does it exist??. Ann Indian Acad Neurol 2022;25:1235-6

How to cite this URL:
Shaik RS, Manorenj S, Rao RV. “Neuroleptic malignant syndrome (NMS) sans rigidity”……Does it exist??. Ann Indian Acad Neurol [serial online] 2022 [cited 2023 Feb 6];25:1235-6. Available from:

Dear Sir,

Neuroleptic malignant syndrome (NMS) is an infrequent and life-threatening adverse effect of antipsychotics, especially the typical antipsychotics.[1] NMS is characterized by delirium, muscular rigidity, fever, and autonomic nervous system dysregulation,[1] as shown in [Figure 1]. A meta-analysis showed an overall estimate of 0.991 cases per thousand people.[2] Various criteria have been designed to improve the diagnostic accuracy of the same.[1] However, NMS remains a diagnosis of exclusion, and atypical forms of NMS exist.[3] Though the presence of rigidity and elevated levels of creatinine kinase (CK) characterize the illness, they are not specific for NMS.[3] A normal CK level and absence of rigidity does not rule out NMS.[4]
Figure 1: Pathophysiology of neuroleptic malignant syndrome (NMS)

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A 20-year-old lady with history of schizophrenia of five years' duration presented to the emergency room (ER) with history of intentional excessive consumption of olanzapine (20 tablets). On examination, the patient was obtunded, dehydrated with a poor Glasgow Coma Scale (GCS – 5), pupils bilaterally sluggishly reacting to light and mute plantar response (bilateral). However, there was no rigidity or any other localizing signs, and no signs of meningeal irritation. Her vitals showed a blood pressure of 90/60 mm Hg, temperature 101 F, pulse rate 145/min, respiratory rate of 35/minute. In view of her GCS, she was intubated and started on supportive medication. With a history of consumption of a large dose of olanzapine, a diagnosis of NMS was considered. She was evaluated to have leukocytosis (cultures negative and no focus of infection) and borderline elevation of CK levels. Troponin I levels and urine for myoglobin were negative. Other lab parameters, CT brain and chest X-ray were all normal. The patient qualified to the diagnosis of NMS according the Nierenberg criteria (though not satisfying DSM-V criteria).[1] Other NMS mimics were ruled out with appropriate investigations.

She was given bromcriptine at the dose of 2.5 mg every sixth hourly through nasogastric tube considering a possibility of NMS. The patient improved remarkably within 24 hours, where her GCS improved to 15 and her autonomic dysfunction settled rapidly (tachycardia, diaphoresis, and tachypnea).

This case emphasizes on a strong clinical suspicion and early initiation of treatment in patients with slightest suspicion of NMS. Though rigidity and elevated CK levels are a hallmark of NMS, absence of either does not rule out NMS.[5] A probable explanation given by the previous authors, though not very satisfactory, is that in the absence of rigidity, CK levels may remain normal.[4] CK levels are also affected by other parameters like dehydration, physical exhaustion, etc.[4] Atypical NMS and impending NMS may not have all the features qualifying the diagnostic criteria.[3] This should not delay the initiation of treatment. Dantrolene sodium remains the drug of choice. However, it is not freely available in India, and therefore bromcriptine was initiated as per the protocol and the patient made a remarkable recovery.[1]

To our knowledge, only three cases of NMS with no rigidity and normal CK levels have been described in literature.[4] Thus, the entity “NMS sans rigidity” is a reality, which needs our immediate attention.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.


My family for supporting me, and my patients for always teaching me; my esteemed teachers and my students.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Tse L, Barr AM, Scarapicchia V, Vila-rodriguez F. Neuroleptic malignant syndrome: A review from a clinically oriented perspective. Curr Neuropharmacol 2015;13:395-406.  Back to cited text no. 1
Gurrera RJ, Simpson JC, Tsuang MT. Meta-analytic evidence of systematic bias in estimates of neuroleptic malignant syndrome incidence. Compr Psychiatry 2007;48:205-11.  Back to cited text no. 2
Carroll BT, Surber SA. The problem of atypical neuroleptic malignant syndrome : A case report. Psychiatry (Edgmont) 2009;6:45-7.  Back to cited text no. 3
Disease N. A rare case of neuroleptic malignant syndrome without elevated serum creatine kinase. Neuropsychiatr Dis Treat 2014;10:403-7.  Back to cited text no. 4
Özdemir İ, Kuru E, Safak Y, Tulacı RG. A neuroleptic malignant syndrome without rigidity. Psychiatry Investig 2018;15:226-9.  Back to cited text no. 5


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