An 11-month-old boy was brought to our emergency room by his parents because of the abrupt appearance of sudden, brief body jerks occurring every 3 to 4 minutes throughout the previous hour. His family history was negative for movement disorders and seizures, and the child presented a normal neurological development and had no past history of neurological illness.
The child had a cold for the previous 2 days and a fever for the preceding 12 hours.
At admission, his body temperature was 39.6°C. The clinical and neurological examination was normal, except for upper airway inflammation. There were no signs of meningeal irritation.
During the observation, the child was sitting with extended lower limbs. Repetitive abrupt, brief jerks involving the four limbs were observed, with violent extension and sometimes abduction of the limbs, occasionally associated with axial retropulsion. Sometimes the jerks occurred in a cluster, with a bigger initial jerk, possibly more tonic, followed by close rhythmic jerks with fading intensity. There were no obvious triggers, such as sudden noises, or tactile or painful stimuli. If holding an object at the onset of an episode, the boy would fist his hand, whereas he would open and extend it if free, suggesting a prevalent proximal involvement. The child looked alert, but frightened, during the events, and cried afterward (see Video 1; written informed consent was obtained from the patient's parents for the publication of this video).
The child was admitted to the pediatric neurology department for further investigations. Routine blood tests revealed mild neutrophilic leukocytosis and the urine test was negative, suggesting an upper respiratory tract infection (URTI). During hospitalization, he experienced two other brief clusters of two to three jerks during wakefulness as well as during sleep, respectively, with a body temperature of 37.5°C and 38.6°C. After administration of ibuprofen, body temperature dropped and myoclonic jerks completely disappeared. A 24-hour video EEG monitoring performed subsequently showed normal background activity in wakefulness and sleep without any epileptic abnormalities and discharges. No episodes were recorded.
The URTI did not require antibiotic therapy, and the baby fully recovered within 2 days with antipyretics. He has remained well over a 24-month follow-up: No neurological deficits, seizures, or psychomotor developmental delay have been observed. Therefore, on the basis of published descriptions of similar fits in infancy,[2, 9] the diagnosis of FM was formulated.
The clinical picture of our patient shows significant similarities to previously reported cases of FM.[5-8]The analysis of the video that we provide will possibly help the diagnosis of FM be easier and more straightforward to make for clinicians.
Although the first 5 cases of myoclonus associated with fever were described in 1960, only 25 patients have been reported in the English literature thus far, none with video documentation of the spells.[5-8] Most likely, FM occurs more frequently than reported, and, at presentation, its distinction from other conditions (such as Fejerman syndrome, epileptic spasms, epileptic myoclonus, or other symptomatic myoclonus[9, 10]) may be challenging for general pediatricians.
As far as our patient is concerned, the absence of a history suggestive of remote or recent brain injury, along with the normal neurological development and exam, make the diagnosis of symptomatic myoclonus extremely unlikely. Moreover, the normal EEG background activity and the absence of photosensitivity, as well as jerks induced by tactile or acoustic stimuli, allow us to rule out also the diagnosis of epilepsy, such as benign myoclonic epilepsy of infancy and infantile spasms. Furthermore, the distinctive occurrence of myoclonic jerks only during fever makes the diagnosis of benign myoclonus of early infancy (Fejerman syndrome), shaking body attacks, or other paroxysmal nonepileptic phenomena unlikely; indeed, these conditions share some clinical aspects with FM, but have not been related to fever.
The clinical features of FM may be summarized as follows: (1) sudden onset of generalized/segmental myoclonus; (2) presence of fever; (3) presentation between 6 months and 6 years of age; (4) nonprogressive course and absence of other additional signs or symptoms; (5) absence of possible causes for secondary myoclonus (hypoxia, metabolic disorders, drug intoxication, storage disease, or neurodegenerative disorders); (6) absence of central nervous system infection; and (7) recovery with cessation of the febrile event in a child with otherwise normal neurological development and physical examination.
Even though the etiopathogenesis remains unknown,[5, 8] the febrile myoclonic jerks in these children do not seem to be related to cortical epileptic discharges.[5, 12] Some researchers suggest a brainstem origin of myoclonus.
The diagnosis is based on careful clinical evaluation. Extensive investigations, such as brain MRI and lumbar puncture, are not necessary for this diagnosis; video EEG polygraphy recordings can be useful to show normal background activity and rule out the epileptic nature of the jerks; benign long-term outcome offers further support to the diagnosis of FM. No therapy is required.
By publishing, for the first time, a suggestive video recording of FM, we draw attention to the importance of increasing the knowledge about this disorder among child neurologists and pediatricians, in order to facilitate its recognition, avoiding misdiagnosis and unwarranted treatment as well as allowing reassurance of parents and caregivers.