March 2011
Dr Gerhard Steenkamp

The past 2 months I have spent some time on diagnosing specific conditions related to the temporo-mandibular joint (TMJ). Sometimes TMJ disease is very subtle and it ends up as one of your differential diagnoses to rule out. A patient may for instance present with pain on opening the jaw.

a   How would you approach the case described?
b   Give 10 differential diagnoses (DD) for this clinical presentation
c   Give the diagnostic tests or diagnostic imaging tests you can perform to differentiate amongst your DD list.

a   A thorough history will be most helpful. Questions I will ask include:
     When did it start?
     Is the pain constant or intermittent?
     What is the patient’s diet?
     What toys/chews does he play with or eat?
     Does he do any manwork?
     Is he painful when eating?
     Is he painful when yawning or barking?

Secondly you need to do a full clinical examination after which you must perform a closer examination of the head. I will concentrate on trying to elicit pain on palpation of the muscles and bony prominences of the head. My last evaluation will be to try and open the mouth to see if it can open and to what extend. The latter evaluation should be done with extreme caution as some of these patients may be very painful indeed and snap at you.

b  Molar abscess causing pressure below the eye and very painful on opening the jaw.
    Condylar fracture
    Masticatory muscle strain due to excessive manwork
    Masitcatory muscle myositis
    TMJ degenerative joint disease
    TMJ neoplasia
    Open mouth jaw locking
    Jaw fracture
    Zygomatic arch fracture
    Craniomandibular osteopathy

c Skull radiographs

The most commonly done views are the dorsoventral or ventrodorsal
views as well as a standard lateral of the skull.

You can also try to improve visualisation of the condyles by elevating
the nose of the patient approximately 20degrees.

Computed tomography (CT)
CT scans of the skull will be the most useful way to evaluate the TMJ’s

Ultrasound
Ultrasound of the TMJ is commonly used in horses, however the amount of information retrieved by this modality may be limited in the dog.

Fine needle aspiration
In larger breed dogs with DJD it may be helpful to obtain a sample of the joint fluid for evaluation. The needle can be inserted under ultrasound guidance or merely by palpation.

Blocking the joint
To determine if only one or both of the joints are affected, you can instil a local anaesthetic drug, into the joint (usually after FNA) thereby blocking it and you can then determine if that joint is involved.

If not that joint, you repeat on the opposite joint a few days later and reassess again. If still not pain free, it is possible to block both (although this does work, it is rarely used).

Biopsy
Should you suspect TMJ neoplasia a biopsy of the lateral condyle can
be done in large breed dogs, or a condylectomy can be done in order to
obtain tissue for histopathology

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