Abduction Deficit Mimicking Sixth Nerve Palsy due to Metastasis in Systemic Malignancy: Rare Case Report.

Lateral rectus palsy presenting as abduction deficit resulting in diplopia is attributed to neurogenic causes. Metastasis as a cause of sixth cranial palsy is an extremely rare entity but cannot be overlooked. Cases of metastasis to lateral rectus secondary to lung and breast carcinoma have been reported. Primary adrenocortical carcinoma (ACC) metastasizing to lateral rectus muscle is extremely rare. Here, we report a case of ACC arising from the left adrenal gland that presented with left-sided abduction deficit in a 58-year-old male with vasculopathic risk factors. The case highlights the importance of neuroimaging in cases of isolated nontraumatic sixth nerve palsy or in cases with isolated ocular symptoms with associated systemic findings. The fact that all cases of muscle palsies may not be neurogenic and rare causes such as metastatic muscle involvement must be included as a differential diagnosis in suspected cases has been emphasized. Copyright:

Introduction

Binocular diplopia and abduction limitation in the elderly is most commonly caused by sixth cranial nerve palsy as a result of microvasculopathy. This is a self-limiting disease with spontaneous recovery. However, there are cases which must be observed with high index of suspicion for masquerades such as occult systemic malignancies with high morbidity and mortality, as our case reports.

Case Report

A 58-year-old male patient presented with complaints of sudden onset diplopia and drooping of eyelids in both eyes for the past 10 days, associated with occasional blurring of vision. He was a nonsmoker with medical history of hypertension and diabetes. There was no history of trauma. He had generalized weakness of the limbs and breathlessness for the past 1 month. The patient was under investigation for pain abdomen at the time of ocular examination.

Best-corrected visual acuity was 20/20 in both eyes. The anterior segment (no congestion, mass), intraocular pressure, pupillary reaction, and dilated fundus examination were normal in both eyes. On attempted left gaze, limitation of abduction of the left eye (−2) was marked which was painless [Figure 1]. The alternate prism cover test revealed 25 prism diopters of esotropia in primary position. Forced duction test, fatigue test, and ice test were negative. Neurological examination was normal. Systemic examination did not reveal any lymphadenopathy, hepatomegaly, and splenomegaly. B-scan ultrasound of the left eye in orbit mode was suggestive of the presence of an anechoic solid mass 2 mm × 2 mm lateral to the optic nerve [Figure 2]. Myasthenia gravis (MG) in view of generalized weakness and drooping of eyelids was considered but ruled out. A working diagnosis of sixth cranial nerve palsy with suspicion of other etiologies such as intracranial space-occupying lesions, metastasis, inflammatory, and demyelinating disorders needed to be excluded and hence neuroimaging was advised.

Figure 1

A 52-year-old male showing esotropia in primary gaze with limitation of abduction in the left eye

Figure 2

B-scan ultrasonography of the left eye showing an anechoic mass 2 mm × 2 mm near optic nerve shadow

Magnetic resonance imaging (MRI) of the brain and orbit revealed a small nodule in the belly of the left lateral rectus muscle 10 mm × 9 mm [Figure 3]. Contrast-enhanced computerized tomography (CT) scan of the abdomen and pelvis showed a mass of 5.4 cm × 3.9 cm × 3.1 cm in the adrenal gland with smaller nodules in the lungs and lateral rectus muscle [Figure 4]. CT-guided fine-needle aspiration cytology (FNAC) from the adrenal gland was reported as adrenocortical adenoma. Blood investigations reported raised cortisol levels of 16 mcg/dl. His postprandial blood sugar was 248 mg/dl, urea was 49 mg/dl, and creatinine was 1.5 mg/dl. Blood electrolytes and urinary cortisol excretion for 24 h were normal.

Figure 3

Pre-and postcontrast three-dimensional axial T1-weighted fat-suppressed magnetic resonance imaging showing a nodular mass 10 mm × 9 mm within the lateral rectus muscle

Figure 4

Axial contrast-enhanced computerized tomography scan of the abdomen and pelvis showing a mass of 5.4 cm × 3.9 cm × 3.1 cm in the left adrenal gland

The patient was referred to the surgical oncologist for the confirmation of the primary tumor after investigations revealed adrenocortical adenoma in FNAC. Positron emission tomography-CT (PET-CT) scan showed high intake in the left adrenal gland mass as well as nodular lesions in the left lateral rectus muscle and sacrum. Complete resection of tumor with excision biopsy of the metastatic mass in the left lateral rectus muscle was performed. Histopathology showed basaloid tumor cells in cribriform pattern with eosinophilic material consistent with adrenocortical carcinoma (ACC) [Figure 5a and b]. Post resection, the patient had the same degree of abduction deficit in the left eye with vision 20/20 in both eyes. The patient was advised for chemotherapy and regular follow-up. He was planned for surgical correction of esotropia at a later date.

Figure 5

Sheets of basaloid tumor cells having abundant eosinophilic cytoplasm and hyperchromatic nucleus adjacent to muscle fibers (elongated cells) (a) is 10 x and 5 (b) is 40 x

Discussion

Ocular metastasis is a rare entity and to detect it clinically is a challenge.[1] Metastases to the orbit are commonly seen in carcinoma of the breast, lung, gastrointestinal tract, thyroid, and kidney.[2] The rate of orbital metastasis varies from 2% to 3% in patients with systemic cancer and metastasis into the extraocular muscles in isolation is extremely rare. This may be due to an unfavorable environment created to the metastatic cells by continuous eye movements. Unilateral involvement of the extraocular muscles is more common than bilateral cases.[3]

Clinical studies have shown that different cancer types frequently display distinct metastatic patterns, with neoplasms of particular histological types tending to metastasize to specific organs.[4] This is explained by the “seed and soil” hypothesis of cancer metastasis proposed by Paget.[5] Based on this theory, ACC metastasizing to extraocular muscles is a rarity.

The diagnosis of orbital metastasis usually occurs during the routine ocular examination or presenting with ocular signs and established by imaging study before or along with the detection of primary neoplasm. Diplopia (48%) is the most common clinical presentation of orbital metastasis followed by proptosis (26%), decreased vision in (16%) of cases, and rarely ptosis or strabismus.[1] This is because of the mass effect or direct infiltration of the tumor cells.

Unilateral abduction deficit when present in the absence of trauma should be systematically examined and investigated. Maximum cases are because of sixth nerve palsy but thyroid eye disorder, orbital pseudotumor, MG, although rare, are to be ruled out.[6] Ptosis in our patient may be due to the generalized weakness and not due to localized metastasis nor from MG. When older patients present with abduction deficit along with systemic symptoms, generalized weakness and weight loss, the possibility of malignancy must be ruled out.[7] Nair et al. have reported that 6.3% of cases of sixth nerve palsy are due to undiagnosed tumors.[8] In our case, the adrenal mass was the largest and subsequent histopathologic examinations of biopsy from adrenal and lateral rectus confirmed this rare presentation. Usually, in cases of ocular metastases, the prognosis is poor as diagnosis of the primary etiology is lacking.

ACC is a rare tumor usually diagnosed in patients in the fifth or sixth decades.[9] Malignancy of adrenal tumors is established on the basis of metastasis and local invasion.[5] The use of imaging modalities such as CT and MRI facilitates early diagnosis of these so-called incidentalomas. CT scan is confirmatory for 95% of orbital metastasis. PET-CT also provides information regarding size, location, nature of the mass and its relation to musculature and other structures. Nuclear magnetic resonance is highly specific for the exclusion of pseudotumor and metastasis.[3] Treatment of ACC is total resection while chemotherapy is effective in patients with metastasis.[10] This case is a rare instance of metastasis to lateral rectus muscle from the adrenal gland tumor confirmed by radiological and histopathological evidence.

Nevertheless, once local and restrictive pathologies have been ruled out one must look for the rare occurrences. Unilateral abduction deficit, ptosis, or sectorial congestion with abnormal blood investigations should be considered red flag signs to exclude systemic diseases and metastasis.

In conclusion, lateral rectus is an uncommon site for metastasis in adrenal gland carcinoma. Hence, abduction deficit in the elderly should be examined with caution keeping in view the masquerades. Imaging in these cases is necessary and can help in diagnosis.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that his name and initials will not be published and due efforts will be made to conceal his identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.