Taste loss as the sole presenting symptom in Chinese patient with facial onset sensory and motor neuronopathy

Dear Editors, First reported by Vucic in 2006,1 facial onset sensory and motor neuronopathy (FOSMN) syndrome is a rare progressive neurological disease, with a total of 100 patients reported in the literatures worldwide.2 However, no cases have been reported from Chinese centers. The age of onset is usually during the fourth to seventh decade with only one case of childhood onset reported.3 There is a male predominance, with nearly twothirds of cases seen in men, and the disease duration ranges from 1.2 to 46 years with an average duration of 8.2 years.2 Patients of FOSMN initially present with sensory deficits of the trigeminal nerve distribution, followed by rostralcaudal spreading to the scalp, neck, upper trunk, and upper limbs.1 Later in the course of the disease, bulbar dysfunction (dysarthria and dysphagia) occurs. Then, lower motor neuron (LMN) features present, including muscle weakness, atrophy, and fasciculation. Generally, only the lower motor neuron system is involved, while the upper motor neuron involvement is rarely seen.4 Herein, we described a Chinese patient with FOSMN who initially presented with taste disturbance.


Dear Editors,
First reported by Vucic in 2006, 1 facial onset sensory and motor neuronopathy (FOSMN) syndrome is a rare progressive neurological disease, with a total of 100 patients reported in the literatures worldwide. 2 However, no cases have been reported from Chinese centers. The age of onset is usually during the fourth to seventh decade with only one case of childhood onset reported. 3 There is a male predominance, with nearly two-thirds of cases seen in men, and the disease duration ranges from 1.2 to 46 years with an average duration of 8.2 years. 2 Patients of FOSMN initially present with sensory deficits of the trigeminal nerve distribution, followed by rostral-caudal spreading to the scalp, neck, upper trunk, and upper limbs. 1 Later in the course of the disease, bulbar dysfunction (dysarthria and dysphagia) occurs. Then, lower motor neuron (LMN) features present, including muscle weakness, atrophy, and fasciculation. Generally, only the lower motor neuron system is involved, while the upper motor neuron involvement is rarely seen. 4 Herein, we described a Chinese patient with FOSMN who initially presented with taste disturbance.

| C A S E PR E S E NTATI O N
A 72-year-old Chinese man presented to our neurology clinic complaining of progressive loss of taste over 2 years. He was unable to differentiate spicy, salty, or sweet tastes. One month after the onset, he noticed constant tingling and numbness at the tip of his tongue and pain in the peri-oral region, which disrupted his sleep. He was prescribed gabapentin, and the pain was relieved. One year later, he exhibited paresthesia in his right upper limb, followed by muscle atrophy. At the same time, he developed sialorrhea and headache.
One and a half years after initial presentation, he developed dysphagia, hearing impairment, and hyposmia. In the latest 2 months, his dysphagia deteriorated, and he developed dysarthria with losing 5 kilograms of weight. The total timeline of symptom onset is shown in Figure 1A. He sought his medical care in the local hospital and was diagnosed with "progressive bulbar palsy." His family history was unremarkable. Results of complete blood count, creatine kinase, electrolytes, total cholesterol and triglyceride, liver function, renal functions, blood sugar, HbA1c, and C-reactive protein were normal. Nerve conduction study showed sensory nerve action potentials (SNAP) decreased in the right median nerve, ulnar nerve, and both superficial peroneal nerves. In needle electromyography, extensively chronic neurogenic changes were apparent in muscles of the bulbar, cervical, thoracic, and lumbosacral regions. A pulmonary function test showed that his forced vital capacity (FVC) was 59.3%.
Magnetic resonance imaging scans of the brainstem showed no abnormality ( Figure 2). Genetic testing of the whole exome sequence was negative. Abnormal nucleotides repeat expansions of the AR or C9ORF72 genes were negative.

| DISCUSS ION
There have been two cases of FOSMN reported with initially taste disturbances in patients of Caucasian and Japanese descent respectively.
The Caucasian patient was a 42-year-old man with taste sensation loss, paresthesia, and numbness in the peri-oral area. However, his numbness did not progress to the head and neck until 5 years later. while only a few cases also have UMN symptoms. 6 Other reports indicate that the development of UMN signs is associated with more rapid disease progression. 7 Our case also corroborates this association, with examination finding of UMN signs and a more rapid disease course.
Our case met the diagnostic criteria of amyotrophic lateral sclerosis (ALS) according to the revised El Escorial criteria, which may be the reason for initial misdiagnosis. Our case showed no abnormality in magnetic resonance imaging scans of the brainstem. However, recent studies detected neurochemical or glucose-metabolism abnormalities in brain stem and cortex of ALS animals using magnetic resonance spectroscopy, suggesting that the above abnormalities may contribute to early differential diagnosis between patients with ALS and FOSMN. 8,9 It remains controversial whether FOSMN is a neurodegenerative disease, an inflammatory disease, or a mix of pathophysiological mechanisms. Minimal response to immunomodulation therapy with refractory progression suggests that

ACK N OWLED G EM ENTS
The authors would like to thank the efforts of Meiying Zhuang for helping revising the language.

CO N FLI C T S O F I NTE R E S T
The authors declare that there is no conflict of interest.

CO N S E NT TO PA RTI CI PATE
The patient provided written consent for participation.

CO N S E NT FO R PU B LI C ATI O N
The patient provided written consent for disclosure of medical information and images.