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This article explores the clinical features of the "Inverted Brown Pattern," a condition characterized by tight inferior oblique (IO) muscles mimicking superior oblique (SO) muscle underaction. The study focuses on patients with unilateral depression deficiency in adduction and minimal IO overaction. Surgery options including IO muscle weakening and contralateral IR recession propose effective treatments, demonstrating improved ocular alignment. Findings also differentiate the Inverted Brown Pattern from other related syndromes, highlighting its unique surgical strategies and potential outcomes.
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“Inverted Brown pattern”: A Tight inferior oblique muscle masquerading as a superior oblique muscle underaction – clinical characteristics and surgical managementGuyton et alJ AAPOS 2006; 10:565-572
Purpose • To characterize and evaluate surgical management of patients with unilateral deficiency of depression in adduction • i.e. SO underaction, without significant ipsilateral IO overaction
Methods • Retrospective study • Patients with diplopia in downgaze who had • Ipsilat IO muscle weakening • Contralat IR muscle recession • Patients showed unilateral deficiency of depression in adduction, suggesting SO muscle underaction, with no or minimal IO muscle overaction • 8PD hypertropia in involved quadrant of downgaze • No more than 6-7PD of overelevation in adduction
Results • 12 pts • 3 had prev surgery for Brown syndr • 4 had prev orbital floor trauma • Exaggerated forced duction testing • Recorded for 9 pts (other 3 not recorded) • Tight IO muscle recorded for 7pts (78%), with no laxity of SO tendon
Results continued • 12 pts • 4 had contralateral IR muscle recession • But in all 4, deficiency of depression in adduction recurred • Ave FU 16mo (7wks to 5yrs) • 8 had IO muscle weakening procedure • IO recession (5) or • IO denervation & extirpation (3) – for excessive tightness on exaggerated FDT • Achieved overall improvement of ocular alignment • 9 subsequent patients with similar pattern of misaligment treated with IO weakening • Good results
Conclusions • “Inverted Brown pattern” • Caused by tight or inelastic IO muscle • Treatment: • IO muscle weakening procedure • Even though no significant IO muscle overaction • Better results than IR muscle recession
Discussion • “Inverted Brown pattern” not the same as “Reverse Brown Pattern” • “Reverse Brown Pattern” - Jampolsky coined the term to describe cases of • Thyroid myopathy with asymmetric upgaze deficiencies due to asymmetric IR muscle tightening
Discussion • “Inverted Brown pattern” inverted wrt Brown syndrome • Difference: • Y pattern sometimes seen in Brown synd • No Y pattern in “inverted Brown pattern” • Due to less side slip of IO muscle – firmly attached to IR muscle sleeve whilst more slip occurs with SO tendon causing Y pattern
Discussion • Customary treatment for apparently underacting SO with no or minimal IO overaction • Ipsilateral SO tuck or • Contralateral IR recession • Consider IO muscle weakening • Good results (small numbers, no longterm follow-up) • Analogous to Brown Syndrome • Low complication rate (rare fat adherence syndrome)
