Temporomandibular Joint (TMJ) Disorder: The pain starting behind the ear and radiating down the neck into the shoulder is consistent with TMJ disorder, which often presents with referred pain to the ear, neck, and shoulder due to the complex innervation of the TMJ.

Cervical Spondylosis or Cervical Radiculopathy: These conditions can cause neck pain that radiates to the shoulder and potentially refers pain to the ear region due to the convergence of cervical and trigeminal nerve pathways.
Earwax Impaction or External Otitis: Although the pain starts behind the ear, conditions affecting the external ear canal can cause significant discomfort that may radiate or be referred to the neck and shoulder.
Tension Headache: Tension headaches can cause pain that is referred to the ear and neck region, especially if there is significant muscle tension in the neck and shoulder area.

Acute Angle-Closure Glaucoma: Although typically associated with eye pain and vision changes, in rare cases, the pain can be referred to the ear and face. It's a medical emergency requiring immediate attention.
Malignancy (e.g., Temporal Bone Tumor, Metastatic Disease to the Cervical Spine): Although rare, tumors in the temporal bone or metastatic disease to the cervical spine can cause ear pain with radiation to the neck and shoulder.
Giant Cell Arteritis: This condition can cause headache, jaw claudication, and visual disturbances but may also present with ear pain and should be considered, especially in older adults, due to its potential for serious complications like vision loss.

Occipital Neuralgia: Involves the nerves that run from the base of the skull to the scalp and can cause pain that radiates to the ear and neck.
Eagle Syndrome (Styloid Process Syndrome): A rare condition where an elongated styloid process or calcified stylohyoid ligament causes pain in the ear, face, and neck.
Trigeminal Neuralgia: Typically involves one side of the face but can rarely cause ear pain, especially if the auriculotemporal branch is involved.