Brief Answer:
May need to consult Otolaryngologist and Neurologist

Detailed Answer:
Hi,thanks for your query, I have gone through your query.

Hi,you might be suffering from following possibilities:

1.) HMS(Hemi-masticatory Spasm) is a rare unilateral movement disorder and characterized by paroxysmal contractions of jaw-closing muscles, such as masseter.

Chewing, talking, and laughing are the most common triggers precipitating the spasm.
Neurological examination is normal, except for the hypertrophy(enlargement) of the involved muscle or atrophy(reduction in size) in some cases associated with localized scleroderma(characterized by inflammation and thickening of the skin from excessive collagen deposition).

The EMG(Electromyography) finding is helpful in the diagnosis and characterized by irregular bursts of motor unit potentials correlating with muscle spasms.

The cause of HMS is not fully known and is considered to be owing to the result of a problem in the motor branch of the trigeminal nerve.

In such a case ,it would be advisable to consult a Neurologist.MRI Brain may be required to know the cause.Medicines like gabapentin,Carbamazepine or Botulin injection may help in Muscle Twitching.

2.) Lymphnode enlargement-There are about 300 lymph nodes in the head and neck region Normally they are not palpable. During an infection or as a response to inflammation, these lymph nodes enlarge. However they rarely regress to their original size and hence remain palpable thereafter.You might be suffering from Lymphnode enlargement over Masseter muscle which may be of infective/inflammatory origin/or Cancerous.

In such a case ,it would be advisable to consult an Otolaryngologist doctor to do ear,nose and throat examination and find out any cause of infection or inflammation or any cancerous growth.

If the node is cancerous,then it would be hard,non-motile,more than 1 cm in size and it keeps on increasing in size.
Looking at your description of swelling,it does not seems to be cancerous.

I would advise you to go for Ultrasonogram (USG) and USG guided FNAC(Fine Needle Aspiration Cytology)-to find out the cause over swelling over your Masseter muscle.

I would also advise you to quit smoking as it may lead to cancer of the lung, esophagus, larynx, mouth, throat, kidney, bladder, liver, pancreas, stomach,etc.

I hope my answer will help you, take care.

I would be happy to answer if you have any follow-up questions.

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Brief Answer:
USG and FNAC would help to reach the diagnosis.

Detailed Answer:
Hi,Thank you for your reply.

Tumor arising from accessory part of parotid gland might be seen as a swelling over Masseter muscle. Incidence of accesory parotid gland tumor is 70% benign and 30% malignant.Generally it is not attached to the muscle.

If it is a malignant tumor,then the swelling would be hard,irregular margins,infiltrating surrounding tissues,might get attached to masseter muscle,etc.

In your follow-up question,I came to know that you are suffering twitching around eye.
In a parotid gland tumor,Facial nerve(7th cranial nerve) might get affected .
Hemifacial spasm is a condition that affects half of your face. It usually starts with a twitching around one eye.If something presses on the facial nerve somewhere along its course, it can affect how the signals are carried to the face. This may cause muscles to twitch (or contract), or to go into spasm, when you don't want them to.Generally it leads to twitching around the eyes and lips.

Looking at your initial query,I thought that you are suffering from twitching of Masseter muscle which is due to Irritation of Trigeminal Nerve(5th cranial nerve)

It is not neccesary that a cancerous parotid tumor should first metastasize to surrounding tissues before affecting facial nerve.

Ultrasonogram(USG) and Fine needle aspiration cytology(FNAC) would help to reach at the diagnosis of Lump over Masseter muscle.

Hope this answers your query.Take care.

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