Diabetes plus third nerve palsy not always diabetic third nerve palsy.

A 45-year-old female with poorly controlled diabetes mellitus presented to us with acute left-sided frontal headache of 2 days duration. The patient had drooping of the left eyelid and diplopia to near objects, which increased upon looking to the right. On examination, the patient had pupil-sparing complete left third nerve palsy. Other cranial nerves were normal. Magnetic resonance imaging (MRI) brain with contrast and magnetic resonance (MR) angiogram were normal. We made a diagnosis of diabetes-related microvascular ischemic third nerve palsy (MP). One month later during follow-up, the patient continued to have severe excruciating left frontal headache. On examination, she still had complete pupil-sparing left third nerve palsy. Persistent severe pain and lack of improvement of third nerve palsy after 1 month of onset of illness were atypical for diabetes-related MP. So, we proceeded with digital subtraction angiography (DSA) to rule out other causes such as aneurysms and vascular malformation. DSA revealed carotid cavernous fistula (CCF), indirect type.

In adults, the most common cause of acute ocular motor mononeuropathies is MP. MP occurs in the setting of vasculopathic risk factors such as diabetes, hypertension, dyslipidemia, and advanced age.[1] Pain is a common feature of ocular motor cranial nerve palsies from presumed MP. Pain duration in one case series ranged from a few days to greater than 2 months, but tended to be longer lasting in patients with more severe pain. In addition to pupil sparing, a chronic stable course associated with spontaneous recovery is suggestive of MP.[2] The presence of pain in both MP and in ocular motor cranial nerve palsies due to compressive lesions underscores the importance of ensuring spontaneous resolution when the diagnosis of MP is made clinically.

CCF is an abnormal communication between the cavernous sinus and the carotid arterial system. CCFs can be classified by etiology (traumatic vs. spontaneous) and anatomy (direct vs. indirect or dural). The dural CCF may be due to congenital arteriovenous malformation that develops spontaneously, often in the setting of atherosclerosis, systemic hypertension, or connective tissue disease. It consists of a communication between the cavernous sinus and one or more meningeal branches of the internal carotid artery, external carotid artery (ECA), or both. The posteriorly draining dural CCF most commonly presents with cranial nerve palsies. The onset of the paresis is sudden, and only one of the ocular motor nerves is affected. The third nerve is most often affected, and the resulting paresis may be complete with involvement of the pupil or incomplete with or without pupil involvement. But almost all cases are associated with ipsilateral orbital pain.[34]

In our patient, even though the pupil was not involved, failure of spontaneous resolution of third nerve palsy and progressive worsening of pain were atypical for MP, and hence, we performed DSA to rule out aneurysm or vascular malformation. DSA revealed indirect CCF (type IV) on the left side with feeders from the meningeal vessels of bilateral internal maxillary arteries. The feeders were embolized using embospheres [Figures 1–3]. After the procedure, the patient was completely relieved of her pain and her third nerve palsy partially recovered during follow-up. Ophthalmoplegia in dural CCF may be caused by swelling of extraocular muscles due to venous congestion, ischemia of cranial nerves by vascular steal phenomenon, enlarged sinus causing compression, or a combination of one or more of the above mechanisms.[5] In our case, since DSA proved it to be posterior draining fistula which has minimal or no venous congestion, we believe that she suffered more ischemia than compression of third nerve, which might probably explain pupil sparing.

Figure 1

DSA AP view. Pre-procedure: Left ECA injection; arterial phase: Showing abnormal early filling of left cavernous sinus (normally cavernous sinus filling will occur only in the later venous phase). Early filling indicates left cavernous sinus has abnormal communication with the arterial system

Figure 3

DSA true lateral view. Post embolization: Left ECA injection; arterial phase: Obliterated fistula and non filling of cavernous sinus

DSA true lateral view. Pre-procedure: Left ECA injection; Arterial phase: showing abnormal early filling of cavernous sinus

In conclusion, dural CCF is an important and treatable cause for painful third nerve palsy which may mimic MP. It is important to diagnose it early, as it is treatable.